Crane and work machine

A crane arrangement includes a base, a pillar boom, a lifting boom, a folding boom, a lifting cylinder, and a folding cylinder. The lifting boom includes a first pivot point for connecting the pillar boom to the lifting boom, a second pivot point for connecting the lifting cylinder to the lifting boom, and a third pivot point for connecting the folding cylinder to the lifting boom. The lifting boom further includes a hollow cast connecting piece arranged at the first end of the lifting boom, in which connecting piece at least the first pivot point and second pivot point are arranged. The invention also relates to a corresponding work machine.

FIELD OF THE INVENTION

The invention relates to a crane arrangement, including: a base for attaching a crane to a work machine; a pillar boom attached rotatably to the base; a lifting boom comprising a first end and a second end pivoted at the first end to the pillar boom; a folding boom comprising two ends, the folding boom being pivoted at the second end to the lifting boom, in order to suspend a tool from the crane; a lifting cylinder comprising a third end and a fourth end, pivoted at the third end to the pillar boom and at the fourth end to the lifting boom, in order to operate the lifting boom; and a folding cylinder comprising a fifth end and a sixth end, the folding cylinder being pivoted at the fifth end to the lifting boom and at the sixth end to the folding boom, in order to operate the folding boom, wherein the lifting boom includes a first pivot point for connecting the pillar boom to the lifting boom and receiving moments acting on the lifting boom, a second pivot point for connecting the lifting cylinder to the lifting boom, and a third pivot point for connecting the folding cylinder to the lifting boom. The invention also relates to a corresponding work machine.

BACKGROUND OF THE INVENTION

In connection with work machines, cranes are used to load different objects onto the load space of the work machine and unload them from the load space of the work machine. For example, cranes are used in connection with forest machines for lifting trees. For the crane to be able to perform diverse lifting with variable paths of movement in often cramped environments, the crane generally includes at least two, often three consecutively pivoted parts, which form the set of booms of the crane. For example, in Ponsse Oy's crane10using lifting booms and marketed under the product name K90+, shown inFIG. 1a, there is a base110for attaching the crane10to the chassis of the work machine, and three consecutively pivoted parts, which form a set of booms11, i.e. a pillar boom12, a lifting boom14, and a folding boom20. In order to move the booms12,14, and20, there are operating devices24and30between the booms12,14, and20, which create movement in the booms12,14, and20around the pivot points36and41between the booms12,14and20. In addition, the crane includes rotation cylinders114, with the aid of which the pillar boom12can be rotated around its longitudinal axis relative to the base110. The crane10also includes its own pivot points38,40′,37, and39for pivoting the operating devices24and30between the booms12,14, and20. A corresponding construction also appears in the cranes Mesera 92F/92FT 86i manufactured by the Finnish company Mesera Cranes Finland Oy. The folding boom often also includes a telescopic extension, which can be used to alter the reach of the set of booms with the aid of a linear movement.

FIG. 1ashows a crane according to the prior art. It should, however, be understood that, although the details of cranes of the prior art vary between manufacturers, particularly the cranes and cranes' sets of booms used particularly in forwarders from different manufacturers have very largely the same basic construction. The basic construction of cranes has become established and practically no real development has occurred in their geometry.

A problem in the aforementioned cranes is that the pivot points36,38, and40′ in the first end16of the lifting boom14are implemented with the aid of cuts70in the structure of the lifting boom14. Such a construction requires a great deal of welding seam, which increases the possibility of manufacturing errors. On the other hand, also the third pivot point40′ of the operating device30between the lifting boom14and the folding boom20is far from the two other pivot points36and38in the first end16of the lifting boom14, thus increasing the size of the structure to be welded. This also leaves the area of the lifting boom14between the third pivot point40′ and the first pivot point36exposed to the bending forces caused by the load at the end of the folding boom20. The bending forces gradually cause fatigue in the material, finally leading to fractures in the structure of the lifting boom14and thus shortening the operating life of the crane10. In addition, the welded seams cause residual stresses in the structure of the lifting boom while the heat exchange in the material, caused by welding, leads in turn to a partial loss of the strength properties of the materials. Further, making the welded joints is a laborious and time-consuming work stage, which also requires a competent workman.

SUMMARY OF THE INVENTION

The invention is intended to create a crane that is more durable and easily manufactured than the cranes of the prior art. The invention is also intended to create a more reliable work machine than work machines of the prior art.

The crane according to the invention is characterized by a crane, which includes a base for attaching the crane to a work machine, a pillar boom attached rotatably to the base, a lifting boom comprising a first end, a second end and a hollow cast connecting piece arranged at the first end of the lifting boom, the lifting boom being pivoted at the first end to the pillar boom and a folding boom comprising two ends, the folding boom being pivoted at the second end of the lifting boom to suspend a tool from the crane. In addition, the crane includes a lifting cylinder comprising a third end and a fourth end, the lifting cylinder being pivoted at the third end in connection with the pillar boom and at the fourth end to the lifting boom to operate the lifting boom and a folding cylinder comprising a fifth end and a sixth end, the folding cylinder being pivoted at the fifth end to the lifting boom and at the sixth end to the folding boom to operate the folding boom. The lifting boom comprises a first pivot point connecting the pillar boom to the lifting boom and receiving moments acting on the lifting boom, a second pivot point connecting the lifting cylinder to the lifting boom, and a third pivot point connecting the folding cylinder to the lifting boom, wherein at least the first pivot point and the second pivot point and the third pivot point are arranged to the connecting piece and the connecting piece includes an opening for routing conductors through the connecting piece and into the lifting boom.

In cranes according to the invention, the arranging of the pivot points in the cast connecting piece permits the lifting boom to be implemented using fewer welded structures in the pivot points, which facilitates the manufacture of the crane and improves its durability. In the cast piece, the loadings between the pivot points can be lead to the cast piece internally, so that there are no welded seams between the pivot points or at the most highly stressed points. In addition, the cast connecting piece is extremely stiff and is able to withstand effectively the moments acting on the lifting boom. With the aid of the opening, the conductors can be led into the lifting boom without separate openings formed afterwards in the structure of the lifting boom, which would weaken the structure. The arranging of the pivot points in the cast connecting piece permits openings to be formed in the connecting piece, so that hoses can be routed through the connecting piece and inside the boom and through the interior of the boom to the end of the lifting boom.

The third pivot point too is preferably arranged in the connecting piece. The forces acting on the pivot points can then all be directed to the same cast and stiff connecting piece, so that the structure of the lifting boom can be lighter than previously. Thus the tubular beam part of the lifting boom can be implemented without large point loads. This in turn permits the tubular-beam portion of the lifting boom to be implemented using as much as 10-25% thinner materials.

Preferably the second pivot point and third pivot point are arranged relative to a line running between the first pivot point and the pivot point of the folding boom belonging to the second end of the lifting boom, in such a way that the intersection point of the line segment perpendicular to the line running through the second pivot point is located on a line at a distance from the intersection point of the line segment perpendicular to the line running through the third pivot point, which distance is 0-20%, preferably 8-15% of the length of the line, in order to equalize the loading of the crane. By arranging the pivot points relative to each other as described above, the loadings are optimized, as the third pivot point, used to attach the folding cylinder to the lifting boom, moves closer to the first end of the lifting boom.

The principle in the placing of the pivot points in the connecting piece is that the pivot points are located in the cast connecting piece in a way that minimizes the loading of the portion of the connecting piece between the second pivot point and the third pivot point and optimizes the loading of the portion of the connecting piece between the first pivot point and the third pivot point, or optimizes the length of the portion between the first and third pivot points.

The pillar boom preferably includes a fork for attaching the pillar boom to the first pivot point around the connecting piece. Thus the lifting boom is supported on the pillar boom over a sufficiently wide space, thus creating a good moment support.

Preferably the intersection point of the line segment perpendicular to a line running through the third pivot point and the intersection point of a line segment perpendicular to a line running through the second pivot point are located at a distance of 1-20% of the length of the line, defined in the direction of the first pivot point. The pivot points can then be locate close to each other, thus reducing the loadings acting on the connecting piece. The said intersection point are preferably located over a distance of 5-15% of the length of the line, defined from the direction to the first pivot point, again to create a more optimal loading.

The second pivot point is preferably located on the opposite side of the line to the third pivot point, relative to the said line. This too reduces the loadings acting on the connecting piece.

The opening is preferably arranged in the connecting piece between the first pivot point and the third pivot point, the surface of the opening in the connecting piece being parallel to the axes of rotation of the pivot points. In other words, the opening is formed in the end of the lifting boom, but not, however, in the sides of the connecting piece, so that the lifting boom is open at its first end, permitting the conductors coming from the pillar boom to be easily placed and routed through the connecting piece and into the lifting boom.

Preferably the opening is round and has rounded edges. The round shape does not have any corners wherein the conductors might get stuck and the rounded edges ensure that any motion of the conductors against the edges of the opening do not cause damage to the conductors.

In addition to the pivot points, the connecting piece preferably includes side walls, which are parallel to the longitudinal direction of the lifting boom and perpendicular in plane relative to the axes of rotation of the pivot points. The side walls are load-bearing elements in the connecting piece. The connecting piece's side walls can also be arranged at a slant to the axis of rotation of the pivot points, so that the width of the connecting piece changes relative to the height of the pillar boom.

The connecting piece preferably comprises side walls, both of which have at least two support structures between the pivot points, each of which support structures connects at least two pivot points to each other on the same side wall. In other words, each structure connects at least one of the following: the first pivot point to the second pivot point, the first pivot point to the third pivot point, the second pivot point to the third pivot point, in order to transmit forces. With the aid of the support structures, the loadings between the pivot point can be transmitted between the pivot points, thus minimizing bending between the pivot points in each side wall of the connecting piece.

According to a first embodiment, the connecting piece is a unified cast piece. It can then be implemented completely without welded seams or other joints, so that it is structurally extremely durable. In addition, the manufacture of the connecting piece is simple compared to a welded sheet-metal structure consisting of many parts, and the cast piece can be made in a single individual work stage.

According to a second embodiment, the connecting piece is formed by combining at least two cast pieces. Casting as two pieces facilitates the casting event of the cast pieces, but on the other hand requires the cast pieces to be combined to form the connecting piece, requiring welding or other joining means.

The connecting piece can include side walls and second openings on both side walls of the connecting piece for handling and connecting the connectors of the conductors to the lines containing in the lifting boom. Thus the connection and tightening of the connectors is easy and can be easily performed through the second opening without special tools.

The first pivot point, the second pivot point, and the third pivot point can be placed in the connecting piece in such a way that a triangle is created between the pivot points when the lifting boom is seen from the direction of the axis of rotation of the pivot points, which the triangle's largest angle α is at most 120°, preferably 60°, when angle α is at the location of the second pivot point, when the locations of the first pivot point and the third pivot point determine the size of the angle. All three pivot points are then close to each other, so that the size of the cast connecting piece also remains reasonable. This means that the casting of the piece is easier and more economic, with good casting and quality properties.

At the second pivot point, the triangle's angle is preferably 60-100°, most preferably 75-90°. The pivot points are then located very close to each other and the length of the cast connecting piece can be as little as 40-60 cm.

The crane's folding cylinder is preferably extended. Thus the third pivot point can be closer to the first end of the lifting boom as part of a compact connecting piece.

The folding cylinder preferably includes an extension for connecting the folding cylinder to the third pivot point. With the aid of the extension, the folding cylinder can be attached to the third pivot point in the connecting piece at the first end of the lifting boom without increasing the cylinder's displacement.

The lifting boom preferably includes a box-type structure. Thus it can be implemented as a relatively light structure.

Both the connecting piece and the box structure of the lifting boom preferably include connector surfaces for joining the connecting piece and the lifting boom to each other. The connecting piece and the lifting boom are reliably joined with the aid of the connector surfaces.

The connector surfaces in the side walls of the boom between the box structure of the lifting boom and the connecting piece can be sinuous in order to minimize the changes in stiffness. The joint is then made as homogeneous and reliable as possible.

There is preferably an extended transfer cylinder in the work machine. With the aid of the extended transfer cylinder the folding boom can be attached directly to the connecting piece of the lifting boom of the crane, though the third pivot point is located farther than usual from the folding boom.

According to one embodiment, the crane includes a lifting grab for gripping a tree, or a processing head for both gripping a tree and processing the tree. For such a purpose the leading of the conductors through the connecting piece can be implemented flexibly, as the conductors' connectors can be tightened through the second openings.

The lifting cylinder preferably includes a jacket and a piston rod, the third end of the lifting cylinder being formed in the piston rod and the fourth end in the jacket, and the folding cylinder includes a second jacket and a second piston rod, the fifth end of the folding cylinder being formed in the second jacket and the sixth end in the second piston rod. Thus sufficiently large forces are created for lifting a heavy load.

The folding boom can be telescopic. In the crane according to the invention a good reach is achieved by means of the telescopic folding boom.

The first pivot point is preferably farther from the pivot point of the folding boom than the second and third pivot points. The lifting of the lifting boom then takes place by extending the lifting cylinder, when its power production is effective.

The length of the connecting piece can be 10-40%, preferably 15-25% of the length of the lifting boom. Its weight then remains reasonable.

The width of the connecting piece at the first pivot point can be 70-100% of the distance between the first and second pivot points. The first pivot point will then be sufficiently wide to effectively withstand the moments acting on the lifting boom.

The width of the connecting piece at the first pivot point can be 5-20%, preferably 10-17% of the length of the lifting boom. The first pivot point will then be sufficiently wide to effectively withstand the moments acting on the lifting boom.

The connecting piece preferably includes a third opening arranged between the first pivot point and the second pivot point, a surface of the third opening in the connecting piece being parallel to axes of rotation of the first pivot point, the second pivot point and the third pivot point wherein the fourth end of the lifting cylinder is attach through the third opening to the second pivot point of the connecting piece of the lifting boom. In other words the connecting piece forms a fork-like structure for the fourth end of the lifting cylinder to attach to the second pivot point of the connecting piece. The purpose of the third opening is also to lighten the structure of the connecting piece as well as function as passage for sand pins used during casting.

The length of the third opening in the length direction of the lifting boom between the first end and the second end is 1.5-3.0-times the length of the fourth end of the lifting cylinder in the length direction of the lifting boom. This enables the fourth end of the lifting cylinder to clear the edges of the third opening without touching them in extreme positions of the lifting boom.

Preferably the third pivot point is lug-shaped. The lug-shaped third pivot point is stronger and easier to manufacture than a fork-type pivot point used in the prior art.

Preferably the lifting boom includes the connecting piece forming the first end of the lifting boom, the box structure having a seventh end and eighth end attached to the connecting piece from the seventh end, and a second connecting piece attached to the eighth end of the connecting piece, the second connecting piece forming the second end of the lifting boom. This enables the more complex connecting piece and second connecting piece to be formed as cast structure while the simple box structure can be a welded sheet metal structure.

Preferably the second connecting piece includes a fourth opening for routing the conductors routed inside the lifting boom through the opening outside the lifting boom.

Preferably the connecting piece is machined so that the thickness of the side walls of the connecting piece correspond to the thickness of the box structure.

The connecting piece is preferably made of steel by casting, which steel has a yield strength of 1650-2000 N/mm2. Thus the connecting piece is strong.

The crane according to the invention is characterized by a work machine, which includes a crane, a tool attached to the crane and conductors routed through the opening of the connecting piece and into the lifting boom, which crane is a crane according to the invention according to any of the aforementioned embodiments. By using the crane presented in this application the conductors can be routed inside the lifting boom of the crane.

Preferably conductors are hydraulic conductors.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1bshows a work machine100according to the prior art, to which a crane10according to the prior art is attached. In the figure, the work machine100is a forest tractor. The crane10can be mounted on the chassis104of the work machine100and a tool102is preferably suspended from the crane10at the end of the crane's10folding boom20. The folding boom20preferably also generally comprises an extension, which can be moved telescopically from inside the folding boom, using a linear movement in the longitudinal direction of the folding boom. The tool102can be, for example, a grab106according toFIG. 1b, or a harvester head, which is suspended from the folding boom20by means of a rotation device108. It can be seen fromFIG. 1bthat the third pivot point40′ connecting the folding cylinder30to the lifting boom14is located quite far from the first pivot point36and the second pivot point38, which are located at the first end16of the lifting boom14.

FIGS. 2a-2cshow the crane10according to the invention. InFIG. 2b, the crane10is attached to the chassis104of the work machine according to the invention and inFIG. 2cin turn to a work machine100according to the invention. According toFIGS. 2a-2c, the crane10according to the invention includes a base110, a pillar boom12, a lifting boom14, a folding boom20, a lifting cylinder24, and a folding cylinder30. The lifting boom14includes a hollow cast connecting piece42, in which at least the first pivot point36and second pivot point38are formed, and preferably also the third pivot point40. When operating the crane10, considerably greater forces act on the first pivot point36and second pivot point38than on the third pivot point, which can also be implemented with the aid of cuts according to the prior art directly on the lifting boom, as shown inFIG. 2bby the reference number40′. In the present application, the term pivot point refers to pivot points the axes of rotation of which are, in the operating position essentially horizontal, or in other words transverse to the longitudinal direction of the pillar boom, the lifting boom, and the folding boom. In the crane10according to the invention, the lifting cylinder24preferably includes a jacket94and a piston rod95according toFIG. 2a. A third end26of the lifting cylinder24is formed in the piston rod95and a fourth end28in the jacket94. The folding cylinder30includes a second jacket96and a second piston rod97and a fifth end32of the folding cylinder30is formed in the second jacket96and a sixth end34in the second piston rod97. In this way using the crane large forces are produced when extending the lifting boom and folding boom.

The crane10is attached to the chassis104of the work machine100with the aid of a base110and the pillar boom12is attached rotatably, for example, to the base110on top of the chassis104of the work machine100, from the ninth end12.1belonging to the pillar boom12. The lifting boom14, comprising a first end16and a second end18, is pivoted to a tenth end12.2belonging to the pillar boom12. The lifting boom14is pivoted from the first end16to the pillar boom12by means of pivot point36. The folding boom20comprises two ends, with the aid of the eleventh end20.2of which a tool108is suspended on the folding boom20or on a telescopic extension to the folding boom (not shown in the figures). The folding boom20can be suspended in the middle with the aid of a pivot structure25at the second end18of the lifting boom14. The pivot structure25can be an arrangement like that known from the prior art, in which the sixth end34of the folding cylinder30is connected with the aid of a fifth pivot point39to an intermediate arm66, which is in turn pivoted at the tenth end to the folding boom20and between which ends a second intermediate arm68is pivoted, which is, in turn, pivoted from the twelfth end to the second connecting piece74.

Between the pillar boom12and lifting boom14is pivoted a lifting cylinder24comprising the third end26and the fourth end28, of which the third end26is pivoted to a fourth pivot point37belonging to the pillar boom12and the fourth end28in turn to the lifting boom's14second pivot point38. The rotation of the lifting boom14around the first pivot point36relative to the pillar boom12is achieved with the aid of the lifting cylinder24. Between the lifting boom14and the folding boom20is pivoted a folding cylinder30comprising the fifth end32and the sixth end34, of which the fifth end32to the third pivot point40of the lifting boom14and the sixth end34is pivoted to the fifth pivot point39of the folding boom20. The rotation of the folding boom20around the pivot point41of the folding cylinder of the lifting boom belonging to the lifting boom14relative to the lifting boom14is achieved with the aid of the folding cylinder30. According toFIGS. 2a-2c, the folding cylinder30is preferably considerably longer than in the crane10according to the prior art of the embodiments ofFIGS. 1aand 1b. This is due to the fact that in the crane10according to the invention the third pivot point40is closer to the first end16of the lifting boom14, so that the folding cylinder30should be longer.

Unlike in the prior art, in the crane according to the invention at least the first pivot point36and the second pivot point38, as well as preferably also the third pivot point40are formed, according toFIG. 3as part of a connecting piece42, which is a hollow cast structure. In the crane10according to the invention the lifting boom14is preferably formed of three separate piece, namely the connecting piece42, a second connecting piece74and a box structure84in between the connecting piece42and the second connecting piece74. The welded box structure84of the lifting boom14, known from the prior art, preferably terminates already before the first end16and the second end18of the lifting boom14and is continuous in the middle of the lifting boom14, except for the ends16and18. The box structure84has a seventh end77attached to the connecting piece42and eighth end79attached to the second connecting piece74shown inFIG. 3. In the prior art, the box structure84, as a welded construction, has been continuous over the whole length of the lifting boom14, so that the pivot points36,38, and40of the lifting boom's14first end16have had to be formed with the aid of separate welded wafers70. In the crane10according to the invention, the connecting piece42is attached to the box structure84of the lifting boom14, in order to form the first end16of the lifting boom14. Preferably the second connecting piece74is attached to the box structure84, thus forming the second end18of the lifting boom14.

According to the invention, the connecting piece42is formed by casting, so that it is structurally strong. The connecting piece is preferably a single cast piece54, but it can also be formed of two separate cast pieces, which are joined together preferably by welding. The connecting piece42preferably includes all the pivot points connecting to the first end16of the lifting boom14, i.e. the first pivot point36, the second pivot point38, and the third pivot point40. In addition, the connecting piece42also includes side walls55, in which the second openings56are formed, and a surface part55.1and a bottom part55.2(shown inFIGS. 4aand 4b). Formed in the same cast piece, the forces between the pivot points36,38, and40are transmitted along the cast structure of the connecting piece42over quite a short distance, so that the lever arms of the forces are short and the torques acting on the connecting piece remain considerably smaller than in solutions of the prior art.

According toFIGS. 4aand 4b, the connecting piece42preferably includes an opening44, through which the conductors46shown inFIGS. 2aand 5bcan be led according toFIG. 2cfrom the pillar boom12through the lifting boom14to the folding boom20and through it to the tool108. The opening44is preferably formed in such a way that it forms an opening in the channel-like structure formed by the box structure84of the lifting boom14at the first end16of the lifting boom14. According toFIG. 4a, the opening44can be at a slight angle relative to the longitudinal transverse direction A of the lifting boom14, when the perpendicular of the place of the opening44lies at a rearward slant relative to the lifting boom14. According toFIG. 4a, the opening44is located on the surface of the connecting piece42between the first pivot point36and the third pivot point40. In this connection, reference to conductors can mean electrical conductors, pressure-medium conductors, such as, for example, hydraulic hoses, or other medium conductors, such as colour-medium hoses. The opening44is round in shape and has rounded edges45shown inFIG. 6a.

In this connection it should be understood that, although in the application the crane's operating devices are described as hydraulic cylinders, which operate in practice hydraulically as part of the work machine's hydraulic system, other kinds of operating device can also be used as the operating devices. In the hydraulic cylinders the pressure medium, i.e. hydraulic fluid, is led into and out of the hydraulic cylinders, inside the system and controlled by the system. On the other hand, the operating devices can be electrical or electro-mechanical operating devices, by which a corresponding linear longitudinal movement is achieved. Further, alternatively the operating device can be a hydraulic cylinder, which comprises its own hydraulic circuit together with pumps and receives its energy as electricity along conductors. The hydraulic circuit is then controlled and operated electrically, when the system of the operating device operates by electrical energy and converts the electrical energy to a flow of pressure medium.

In addition to the opening44, the connecting piece42preferably also includes the third opening82shown inFIG. 4b, which is located in the connecting piece42on the surface between the first pivot point36and the second pivot point38, preferably in the bottom part55.2of the connecting piece42. In other words, the third opening82is in the undersurface of the lifting boom14, when the lifting boom14is horizontal. The third opening82preferably also forms a route, along which the fourth end28of the lifting cylinder24is placed inside the connecting piece42and attached through the connecting piece42. The connecting piece42is then on both sides of the fourth end28of the lifting cylinder24and the fourth pivot point37is formed between the lifting cylinder24and the pillar boom12. In other words, the connecting piece42forms a lug for the fourth end28of the lifting cylinder24. The crane's booms rotate around a vertical axis with the aid of rotation cylinders114which are located in the base110. The base is in turn attached to the chassis104of the work machine100and the pillar boom12rotates on top of the base110.

FIG. 5ashows a side view of the lifting boom14of the crane according to the invention.FIG. 5ashows the connector surfaces80.1and80.2between the connecting piece42and the box structure84of the lifting boom14, by means of which the connecting piece42and the box structure84are joined to each other. The connector surfaces80.1and80.2are preferably welded to each other, in order to create a permanent joint. The connector surfaces80.1and80.2are sinuous in the transverse direction relative to the longitudinal direction of the lifting boom14, in order to create a long welded seam, the length of which and the curves appearing in it, i.e. the points80.5, prevent rapid changes in the stiffness in the lifting boom14in the longitudinal direction of the lifting boom. The second connecting piece74too can be attached to the box structure84of the lifting boom14with the aid of a sinuous connector surface80.3and80.4. The second connecting piece74preferably includes a fourth opening75shown inFIGS. 4aand 4bthrough which the conductors46routed inside the lifting boom14through the opening44can be led out of the lifting boom and onwards to the folding boom20.

According toFIG. 5a, the side walls55of the connecting piece42can include second openings56for connecting the connections90of the conductors46shown inFIG. 5b. In other words, the plane of the second opening56is vertical. With the aid of the second opening56, the operator can easily connect the connectors90of the conductors46coming from the pillar boom12to the conductors46running through the lifting boom14, as the connectors90can be easily accessed through the second opening56. When referring to the second opening56it should be understood that on both sides of the connecting piece42there is a single second opening, so that at this point in the connecting piece42a direct connection is formed through the connecting piece42in the transverse direction of the lifting boom14. Here it should also be understood that the openings of the connecting piece42, i.e. the opening44, the second opening56, and the third opening82all also lighten the weight of the connecting piece42and bring savings in materials. The surroundings of the openings are strengthened with reinforcements, which can be formed, for example, by using a thicker material around the openings than elsewhere in the connecting piece.

FIG. 5bshows a side view of the lifting boom14of the crane according to the invention and as a cross-section along the centre line A-A ofFIG. 4b.FIG. 5cshows a cross-section C-C slightly to the side of centre line A-A. According toFIG. 5c, on both side walls55of the connecting piece42relative to the centre line A-A of the lifting boom14a support structure52is formed between at least two pivot points36,38, and40, which reinforces the connecting piece42and acts as a force-transmitting element in the connecting piece42. More specifically, the support structure52is preferably a thicker layer of material than the thinner structures of the connecting piece, which when transmitting forces connects at least two pivot points to each other. According to one embodiment, all the pivot points are mutually joined together by the support structures. More specifically, the surrounding of the openings of the shaft of each pivot point is a reinforced structure, in which the material thickness is greater. The support structure52is also clearly visible inFIG. 5c, in which the longitudinal cross-section of the lifting boom14is made along the cross-section C-C ofFIG. 6anext to the centre line.

Returning toFIG. 5a, the location of the first pivot point36, the second pivot point38, and the third pivot point40in the connecting piece42is preferably such that, seen from the side the pivot points36,38, and40form a triangle60, which is shown in the figure by broken lines. The triangle's60largest angle α, which is at the second pivot point38can be at most 120°, but preferably 60-100°, most preferably 75-90°, the locations of the first pivot point36and the third pivot point40determining the magnitude of the angle. The pivot points36,38, and40are then located close to each other, thus permitting smaller external dimensions of the connecting piece42and thus shorter moment arms in the case of the forces acting on the connecting piece through the various pivot points. In the case of the second pivot point38the angle of the triangle60is preferably 85-95°. The second pivot point38and the third pivot point40are then essentially on top of each other vertically when the lifting boom14is horizontal. This in turn permits the creation of a sufficiently large opening44between the first pivot point36and the third pivot point40and the placing of the third pivot point40slightly closer to the folding boom20. The placing of the third pivot point40closer to the folding boom20for its part permits a slightly shorter structure in the folding cylinder30.

InFIG. 5d, the connecting piece42and the second connecting piece74are shown as being exaggeratedly close to each other, so that the intersection point p1and p2of the line z between the first pivot point36and the pivot point41of the folding boom of the lifting boom and the line segments j and k drawn perpendicularly to it from the second pivot point38and the third pivot point40can be clearly seen. In reality, the connecting piece42and the second connecting piece74are far from each other, according toFIGS. 5aand 5b. According to the figure, the distance d between the intersection points j and k is preferably 0-20% of the length of line z.

According toFIGS. 1band 2b, in the crane10according to the invention the folding cylinder30is longer than in cranes10according to the prior art, as the attachment of the folding cylinder30to the third pivot point40of the lifting boom14is located in the crane10according to the invention closer to the first end of the lifting boom14that in cranes according to the prior art. The displacement of the folding cylinder can correspond to that in the prior art, but the folding cylinder30preferably includes an extension98according toFIG. 2a, so that the folding cylinder30reaches the third pivot point40of the connecting piece42.

Preferably, the connecting piece of the crane according to the invention has a length of 50-100 cm, a width of 20-50 cm, and a height of 50-80 cm. The thickness of the sides of the connecting piece can be, for example, 10-25 mm. The steel used can be, for example, steel manufacture by the Swedish company SSAB and known under product name Strenx 650, or similar, which has a yield strength of 1650-2000 N/mm2. The connecting piece can be made by core casting. In the casting stage of the connecting piece, the mould preferably includes two halves, of which in the first there is a mould and core, and in the second the second half of the mould. In casting, the core is supported through openings inside the hollow pieces with the aid of sand pins, and when the cast connecting piece has hardened the core is vibrated out from inside the hollow pieces. The holes do not weaken the connecting piece's structure, as they are located at places where large stresses naturally do not form.

According toFIGS. 2a-2c, the fourth end28of the lifting cylinder24is attached to the second pivot point38of the connecting piece42, which is fork-shaped, i.e. the fourth end of the lifting cylinder24goes inside the connecting piece. On the other hand, the first pivot point36and the third pivot point40are, in turn, lug-shaped, i.e. the tenth end12.2of the pillar boom12includes, according toFIG. 7, a fork92, which is intended to receive moments acting on the lifting boom. The fork is 150-500 mm, preferably 250-350 mm wide. With the aid of the wide fork, the moments acting on the lifting boom are effectively transferred to the pillar boom with the aid of the stiff connecting piece.

The crane's lifting boom's length can be 150-300 cm, its height 15-30 cm, and its width 20-40 cm. The folding boom can be of the same order of size as the lifting boom. For its part, the pillar boom can be 100-200 cm long, 20-50 cm wide, and 15-30 cm high, is the pillar boom is set horizontally.

In the work machine according to the invention, the crane is controlled using a valve block and control unit belonging to a work machine or crane according to the prior art, with the aid of which the flow of hydraulic oil to the lifting and folding cylinders is controlled. The lifting and folding cylinders are preferably controlled separately.

The crane according to the invention can be used, for example, in forester machines, which can be work machines using a harvester, or forwarders, but also in other applications, such as, for example, in connection with grabs.