Field of the Invention

This invention relates to an .outer-boom crane of the type including a first boom section and an outer boom con¬ nected thereto by a first or main articulation and pivot- able in relation thereto with the aid of a double-acting hydraulic cylinder which is arranged on the upper side of said first boom section and whose one end, e.g. the cylin- der end, is articulated to said first boom section and whose other end, e.g. the piston-rod end, is articulated to at least a first link forming part of a link system which operates between said first boom section and said outer boom and which further includes at least a second link articulated to said first link by a second articu¬ lation and to the outer boom by a third articulation, said first link being connected to the first boom section by a fourth articulation, said outer boom being pivotable rela¬ tive to said first boom section between a first end or starting position on the underside of the first boom sec¬ tion and a second end position on the upper side of a longitudinal centre axis through the first boom section, the main outer-boom working range for lifting and lowering a load being located essentially within the semicircle of the pivotal movement closest to said first end position. Before going into the details of the prior art, it should be pointed out that, basically, a double-acting hydraulic cylinder operates either by pulling or by push¬ ing action. When the hydraulic cylinder operates by pull- ing action, hydraulic oil is supplied to the chamber located on the piston-rod side, and at the same time oil is evacuated from the other chamber, while the length of the hydraulic cylinder is shortened. Inversely, a pushing cylinder operates by oil being pumped into the chamber on the piston side, and at the same time oil is evacuated from the chamber on the piston-rod side, while the cylin¬ der is lengthened. Since the piston rod takes up a certain

amount of space in the associated chamber, the effective pressure area on the piston-rod side is considerably smaller than that on the piston side. This difference in area is especially pronounced when the piston rod, for reasons of strength, has to be relatively thick. Thus, a pulling cylinder must be of much sturdier dimensions than an analogous pushing cylinder in order to be able to exert the same amount of power. Description of the Prior Art A number of outer-boom cranes of the type mentioned in the introduction are previously known in the art (see, for instance, SE 8502014-7). In these prior-art cranes, the link system serves to enable pivotal movement of the outer boom within a working range exceeding 180°, more precisely between a first end position in which the outer boom is parallel and immediately adjacent to the underside of the first boom section, and an opposite second end position in which it is directed upwardly and forms an angle of about 45° with an imaginary extension of the first boom section, i.e., the outer boom can maximally be pivoted about 225° between the two end positions. To this end, there is, in the link system between the outer boom and the first boom section, a comparatively short distance between the main articulation and the fourth articulation connecting the first link to the outer boom, at the same time as both the first and the second link are much longer than this distance. With this geometry, the second link will, when the first link is pivoted by means of the hydraulic cylinder, move in an essentially arcuate path outside of and about the main articulation while trans¬ mitting power to the third articulation which is located in essentially the same plane as the main articulation that is perpendicular to the longitudinal axis of the outer boom, the stretch between the main articulation and the third articulation forming the required moment arm for carrying out the pivotal movement.

Outer-boom cranes of the type described above are advantageously used in forestry work and are usually mounted on the rear end of a lorry or a trailer. These cranes then include a timber grapple mounted at the tip of the outer boom or a projecting member forming part there¬ of, i.e. a two-step or multi-step telescopic boom incorpo¬ rated in the outer boom. The grapple may advantageously be set in a position of rest on the load carrier of the vehicle, at the same time as the first boom section can rest on the load carrier, owing to it being possible to set the outer boom in an upwardly directed position where it forms an angle of about 45° with the first boom sec¬ tion. Another advantage of these prior-art cranes is that the hydraulic cylinder is mounted in a protected position on the first boom section, so as not to be damaged when the first boom section, as often happens in practice, strikes the upright stakes defining the loading space of the vehicle.

However, the prior-art cranes described also have several disadvantages. Thus, the hydraulic cylinder ope¬ rates by pulling action within precisely that part of the working range where the power requirement is at its high¬ est, i.e. in the sector of more than 90° in which the outer boom is pointing outwards from the tip of the first boom section. Together with the fact that the piston rod of the cylinder has to be rather thick for reasons of strength, this means that the cylinder has to be extra¬ ordinarily sturdy, and consequently becomes not only expensive but also heavy. Further, the hydraulic system associated with the cylinder is rendered even more com¬ plicated and expensive by the necessary arrangement there¬ in of so-called lowering control valves. The reason for this is as follows. When the outer boom is to lower a load within the previously mentioned outer working sector, the load has the effect of lengthening the hydraulic cylinder, and the chamber on the piston-rod side tends to be emptied of oil much faster than the chamber on the opposite side

of the piston can be filled with oil. To achieve a balance between the emptying and the filling of the two chambers, use has to be made of special throttle valves regulating the evacuation of oil from the chamber on the piston-rod side in such a manner that the other chamber is filled with an equivalent amount of oil. A further disadvantage of such throttle or lowering control valves is that they easily cause the outer boom to move jerkily, if they do not meticulously regulate the oil flows. Prior-art cranes further suffer from the disadvantage of a restricted range of pivotal movement, namely maximally about 225°. Further, the outer boom cannot be parked in a position where it is parallel to and above the first boom section. Objects of the Invention One object of the present invention is to obviate the drawbacks of prior-art outer-boom cranes by providing a crane in which the hydraulic cylinder can operate by push¬ ing action when the power requirement is at a maximum and in which the hydraulic cylinder thus can be given minimum dimensions for a certain requirement. A further object of the invention is to provide a crane in which there is no need of any special lowering control valves. Another object of the invention is to provide a crane which has a much larger range of pivotal movement than the prior-art outer-boom cranes described. Yet another object of the invention is to provide a crane in which the outer boom can be taken to a parking position close to the upper side of the first boom section, so that the first boom section may in turn be taken to a parking position close to the post or body of the crane when the outer boom is in its parking position. Summary of the Invention

According to the invention, these objects are achiev¬ ed by a crane with the distinctive features recited in the appended claims.

Further Elucidation of the Prior Art

It is true that the prior art embraces outer-boom cranes in which the outer boom can be taken to a parking position parallel and close to the upper side of the first boom section. In these cranes, however, the outer boom is not pivoted with the aid of a single hydraulic cylinder arranged on the upper side of the air cylinder, but with the aid of two cylinders arranged one on each side of the outer boom and the first boom section, respectively. Con- sequently, these cylinders constantly run the risk of being damaged by striking e.g. a stake of a logging truck. Brief Description of the Drawings

In the drawings, FIG. 1 is a side view showing the crane according to the invention in two different positions,

FIG. 2 is a simplified top plan view showing the first boom section and the outer boom of the crane in a substantially horizontal extended position, FIG. 3 is an enlarged side view of the crane, showing the first boom section in a lowered position and the outer boom in a raised parking position, and FIG. 4 is a partial side view showing a modified embodi¬ ment of the invention. Description of the Preferred Embodiments The crane illustrated in Figs 1-3 has a first boom section 1 and an outer boom 2. At its inner end, the first boom section 1 is articulated to a post or body 3 so as to be pivotable in relation thereto by a hydraulic cylinder 4 termed air cylinder. As appears from Fig. 3, the post 3 may, via a live ring 5, be mounted on a supporting girder 7 which stands on legs 6 and which in turn can be mounted on a vehicle chassis as indicated by frame girders 8, 8'. By the live ring 5 or an equivalent device, the post 3 can be turned to different rotational positions relative to the supporting girder 7.

The outer boom 2 is connected to the first boom sec¬ tion 1 by a first or main articulation 9 and can be pivot¬ ed relative to the first boom section with the aid of a double-acting hydraulic cylinder 10 termed outer-boom cylinder, which is situated on the upper side of the first boom section. However, the first boom section 1 is chiefly made up of a box girder 11 whose upper side is designated 11' and whose underside is designated 11", its side flanges being designated 11"' (see Fig. 2). In-analogous manner, the outer boom 2 is chiefly made up a box girder 12 whose upper side is designated 12' and whose underside is designated 12", its side flanges being designated 12"'. At the free end or the point of the outer boom 2 is pro¬ vided a tool carrier 13, which may be mounted either directly on the outer boom or on an extendable telescopic boom incorporated therein. The tool carrier may carry a rotator from which is suspended a timber grapple. Natural¬ ly, the carrier 13 may carry any optional tools.

The hydraulic cylinder 10, which in conventional man- ner includes a proper cylinder member 14 and a piston rod

15, is at one end, in this case the cylinder end, articu¬ lated to the first boom section, and at the other end, in this case the piston-rod end, articulated to a first link

16. The link 16 is part of a link system which operates between the first boom section 1 and the outer boom 2 and further includes a second link 17. The link 17 is con¬ nected to the first link 16 by a second articulation 18 and to the outer boom 2 by a third articulation 19. The first link 16 is connected to the first boom section by a fourth articulation 20. In the preferred embodiment shown, the link system further includes a fifth articulation 21 connecting the first link 16 to the hydraulic cylinder 10, more precisely to the piston-rod end thereof. The cylinder member 14 is connected to the first boom section 1 by a sixth articulation 22.

The outer boom 2 can be pivoted relative to the first boom section 1 between, on the one hand, a first end or starting position A (indicated by broken lines in Fig. 1) on the underside of the first boom section and, on the other hand, a second end position (designated B in Fig. 3) on the upper side of the first boom section. The main outer-boom working range for lifting and lowering a load is located essentially within the semicircle of the pivo¬ tal-movement range closest to the first end position A. It should here be pointed out that the terms upper side and underside are used for conceptual simplicity, and these parts of the first boom section and the outer boom are not always situated respectively above and below one another. Thus, the outer-boom surface or flange 12" termed underside may be turned upwards in relation to the oppo¬ site surface or flange 12' , namely when the outer boom is in the starting position A. The first boom section 1 may also be set in other positions than the substantially horizontal position illustrated in Fig. 1, and strictly speaking the opposite surfaces 11' and 11" thus no longer are the upper side and the underside, respectively.

According to a distinctive feature of the invention, the distance between the third and the fourth articulation 9 and 20 exceeds that between the second and the fourth articulation 18 and 20. Further, the third articulation 19 connecting the second link 17 to the outer boom 2 has been removed from the main articulation 9 and located at least a certain distance out on the outer boom as seen from the main articulation 9. This enables positioning of the second link 17 (or a straight line between the second and the third articulation 18, 19) below the main articulation 9 in order - when the outer boom 2 is within its working range - to pivot the outer boom from the first end or starting position A by lengthening the hydraulic cylinder 10, and to pivot the outer boom in the opposite direction by shortening the hydraulic cylinder. This geometry of the link system makes it possible for the hydraulic cylinder

to lift the outer boom by exerting a pulling action in precisely that part or sector of the working range where the power requirement is the highest, namely in the sector where the outer boom is directed-out from the first boom section, as indicated in Fig. 1.

As appears from Fig. 2, the first link 16 is made up of two halves 16', 16" which are rigidly interconnected by a connecting element 23 and are located one on each side of the first boom section. Also the second link 17 is made up of two halves 17', 17" arranged one on each side of the outer boom and the first boom section, respectively. In the embodiment shown, the connecting element 23 also forms the articulation 21 connecting the link or link halves to the piston rod 15. Thus, the element 23 may consist of a pivot on which is mounted a carrier ring 24 disposed at the free end of the piston rod.

At the outer end connected to the outer boom, the first boom section 1 has two spaced-apart side elements 25, 25' which are inclined relative to the longitudinal or centre axis of the first boom section and project a dis¬ tance upwards from the upper side of the first boom sec¬ tion to position the main articulation 9 away from said longitudinal axis. More precisely, the distance or dif¬ ference in level between the main articulation 9 and an imaginary extension of the upper side 11' of the first boom section perpendicular thereto should be substantially equal to the sum of the diameter of the cylinder member 14 and the distance between the upper side 12' of the outer boom and an axis 26 which is parallel thereto and extends through the main articulation 9. Thus, the outer boom may, as is apparent from Fig. 3, be pivoted to a parking posi¬ tion B forming the second end position, in which it is substantially parallel and close to the hydraulic cylinder which then is located between the outer boom and the irst boom section. In practice, each of the two side elements 25, 25' may be a sheet metal member of wedge-like tapering shape. The thicker or broader end of the individual wedge-

like side member is connected to the first boom section, whereas the narrow end forms an attchment for the main articulation 9. The individual side element may advan¬ tageously, as is seen most clearly in Fig. 3, have, at its free and narrow end connected to the main articulation, an end portion 27 which is downwardly bent a distance in relation to the remainder of the side element to position the outer boom as close to the underside of the first boom section as possible when the outer boom is in the first end position A. It should also be observed that the fourth articulation 20 connecting the first link 16 to the first boom section is close to the underside 11" of the first boom section as well as to the outer side edge 28 of the side elements. In other words, the articulation 20 is immediately adjacent to the transitional area between the underside 11' of the box girder 11 and the outer edges 28 of the side elements 25, 25'. It should further be pointed out that the outer end 29 of the box girder 11 is located at a certain distance inwardly of the main articulation 9 (see Fig. 2), and there is consequently a free space 30 in the area between the articulation 9 and the girder end 29. When the outer boom 2 is pivoted to the first end position A, two reinforcement plates 31, 31' for the articulation 19 can be partially contained in the space 30, more pre- cisely with portions thereof extending downwardly a short distance from the underside 12" of the outer boom. It should further be emphasised that the articulation 19, which in practice may be a throughgoing pivot or tubular member, is positioned at such a distance from the articu- lation 9 that it in the end position A will be located in the transitional area 32 (see Fig. 3) between the bent outer end portions 27 of the side elements 25, 25' and the edges 28.

As appears from Fig. 1, the two articulations 18 and 21 are spaced apart from one another, advantageously a considerable distance along a circular arc whose centre is the articulation 20.

In actual practice, the articulation 19 may advan¬ tageously be located along the imaginary straight line 33 connecting the main articulation 9 to an attachment centre 13' on the tool carrier 13. Owing to the low position of the articulation 19 on the outer boom, the link 17 or link halves 17', 17" act upon the lower half of the outer boom, i.e. below the longitudinal axis 26.

The crane described operates as follows.

In its first end position A, the outer boom forms an angle of about 30° with the first boom section. More pre¬ cisely, the connecting line 33 between the main articula¬ tion 9 and the attachment centre 13' forms an angle of exactly 28° with the first boom section 1. From this end position, the outer boom is movable within its so-called working range which extends through about 180° from the end position A. When the first boom section 1 is set as in Fig. 1, i.e. is directed essentially horizontally out¬ wardly from the post 3, a first sector of about 60° is located to the left of a vertical line through the main articulation 9, and a sector of about 120° is situated to the right of the vertical line. When the outer boom is moved from the end position A, the tool carrier 13 thus moves downwards in the left sector of the working range but will, when swung further into the right sector, move upwards. When in the left sector, the tool carrier is located comparatively close to the post 3, for which rea¬ son the power required for lifting operations in this sec¬ tor is fairly restricted. When lifting a load in the right sector, however, the distance between the load carrier and the crane post is larger, and the power requirement thus is much higher. The power requirement is at a maximum when the outer boom is directed substantially horizontally out¬ wardly from the first boom section.

When the outer boom is in the right sector of the working range and the hydraulic cylinder 10 is lengthened by oil supply on the piston side, at the same time as oil is evacuated from the chamber on the piston-rod side, the

first link 16 will be pivoted clockwise about the articu¬ lation 20, as seen in Fig. 1. By the two links 17', 17", this movement is transmitted to the articulation 19 which applies to the outer boom a force' striving to pivot the latter anticlockwise about the main articulation 9. The lifting moment required to pivot the outer boom about the main articulation is determined by the distance or the leverage between the main articulation 9 and the second link or link halves 17', 17" (or more precisely the straight line connecting the articulation 19 to the arti¬ culation 18). The stronger the leverage, the stronger the lifting moment acting on the outer boom. When the hydrau¬ lic cylinder is further lengthened and the outer boom thus is further swung upwards in this sector, the distance or the leverage between the articulation 9 and the link halves 17', 17" tends to be reduced. However, this ten¬ dency is counteracted by the articulation 18 moving down¬ wards in relation to the articulation 9, in that the first link 16 is swung clockwise about the articulation 20. Thus, a considerable leverage can be maintained between the articulation 9 and the link halves 17', 17" within a relatively large working range, which means that the outer boom, by means of the link system according to the inven¬ tion, can be swung upwards to a relatively high position above a horizontal plane extending through the articula¬ tion 9, when lifting a load.

In that part of the working range where the power requirement is the highest, i.e. the right sector, the hydraulic cylinder may thus operate by pushing action, which, for reasons mentioned in the introduction, is advantageous in so far as the hydraulic cylinder thus can be given minimum dimensions for a given requirement. In the left sector of the working range, the power required for lifting a load is so small that it can be fairly provided for despite the fact that the cylinder operates by pulling action when lifting in this sector.

When pivoting the outer boom upwards in the right sector of the working range, the outer boom finally reaches a neutral or dead-centre position in which the load cannot be lifted any higher, ^' since the first link 16 when pivoting clockwise reaches an end position from which it cannot proceed further (at the same time as the link halves 17', 17" reach the articulation 9). Special mea¬ sures have to be taken to pivot the outer boom from this neutral position to the parking position B of Fig. 3, e.g. to apply the outer boom to a fixed object and fold it, or take the first boom section to an upright position in which the outer boom under the action of its own weight tends to move towards the parking position B. This state, when there is naturally no load, only requires a force determined by the weight of the outer boom and sufficient to swing the outer boom to the parking position. The power generated when the hydraulic cylinder operates by pulling action is completely adequate for this purpose. Thus, the outer boom is swung from the neutral position to the park- ing position by shortening of the hydraulic cylinder, and the link 16 is swung anticlockwise about the articulation 20 at the same time as the link halves 17', 17", after the outer boom has passed the neutral position, pivot the outer boom anticlockwise about the articulation 9. The advantages of the invention leap to the eye. Since the hydraulic cylinder 10 can operate by pushing action when the power requirement is at a maximum, it can be given minimum dimensions and thus be inexpensive to make. For the same reason, there is no need of any special lowering control valves, since a load is lowered in the critical (the right in Fig. 1) sector of the working range by shortening of the hydraulic cylinder, so that oil is evacuated on the piston side and not on the piston-rod side. Further, the pivotal-movement range of the outer boom is much larger than that of prior-art outer-boom cranes. The crane described thus has a pivotal-movement range of about 330°, to be compared with the 225° of the

prior-art cranes of the type described in the introduc¬ tion. In addition, the invention makes it possible to park the outer boom in a position on the first boom section, to which it is then parallel and comparatively close, at the same time as the cylinder retains its impact-protected position on the first boom section, more precisely between this section and the outer boom.

Fig. 4 shows an alternative embodiment of the inven¬ tion, in which the second link (or link halves) 17 are connected to the articulation 21' connecting the piston rod 15 of the hydraulic cylinder to the first link 16. In this case, the articulations 18, 21 are replaced by a single common articulation 21' , which naturally simplifies the making of the link system proper, but also slightly impairs the ability of the outer boom to lift a load high up, since the leverage between the main articulation 9 and the second link here is reduced more quickly when the outer boom is swung upwards. Conceivable Modifications of the Invention It goes without saying that the invention is not restricted to the embodiments described above and shown in the drawings. Thus, the hydraulic cylinder 10 may be so turned that the piston rod is connected to the first boom section and the cylinder member is connected to the link at issue, the embodiment shown being, however, the one preferred. Further, the relationship between the lengths of the first boom section, the outer boom and the crane post can be varied within wide limits, although the embo¬ diment shown is preferred, in which the first boom section is longer than the outer boom proper (when the projecting member is not pulled out) and the crane post, the post and the outer boom being of approximately the same length. Also, the crane according to the invention can be mounted in various ways. Although the fact that the outer boom can be parked on the upper side of the first boom section advantageously permits the crane to be mounted between the driver's cab and a load carrier behind the cab, it is

conceivable to mount the crane in other optional positions, not only on a vehicle but also elsewhere, e.g. on a ship or a stationary structure.