The invention relates to a telescopically extendable girder for a trailer, which girder comprises a first beam with relatively small dimensions in cross-sectional direction which is received slidably in a second beam with relatively larger dimensions in cross-sectional direction, wherein the girder has an underside directed toward the bottom in installed situation and an upper side located opposite, which together determine a height direction of the girder, and wherein the first beam comprises a connecting part enclosed in the second beam and a free end part located opposite. The invention also relates to a trailer which is provided with such a telescopic girder. A trailer with telescopic girder for transport of very long self-supporting loads, such as rotor blades of wind turbines, is for instance known from US 2011/187083 AL

US 2011/187083 Al describes a telescopically extendable trailer having a three-part telescopic girder. A rear beam of the telescopic girder, this having the largest dimensions in cross- sectional direction, is attached to a chassis with four axles. A front beam, having the smallest dimensions in cross-sectional direction, is attached to a gooseneck which is placed onto a pulling vehicle. Arranged between the front and rear beam is a middle beam whereby the length of the trailer in fully extended situation corresponds to that of a rotor blade of a wind turbine. In some shown embodiments the root and the part of the rotor blade connecting thereto are carried on the chassis, and a support is mounted on the girder for a tip part of the rotor blade, this extending above the pulling vehicle. In other embodiments the blade root lies on the gooseneck and the blade tip is carried by a support at the rear of the chassis.

The known trailer is not very suitable for transporting rotor blades in areas where obstacles over the road limit the maximum travelling height, since the root of the blade is carried in all shown embodiments by a surface lying above the wheels and therefore protrudes far above the road surface.

The invention has for its object to provide a telescopically extendable girder of the above described type, whereby a trailer can be formed which, when loaded with a rotor blade, has a smaller travelling height than the known trailer. According to the invention, this is achieved in such a girder in that a dimension of the first beam in the height direction is smaller at the position of or close to the free end part than at the position of or close to the connecting part. Reducing the height of the first beam in the vicinity of the free end part creates additional space above the beam on one side, whereby a rotor blade loaded thereon comes to lie at a deeper position. In addition, this makes the beam easier to deform, causing it to bend relatively further when loaded with a rotor blade, thus limiting the overall height of the loaded trailer even more.

The second beam can here in any case have a closed form in cross-section. The second beam can be prismatic, i.e. have a constant dimension in height direction over its whole length. The free end part of the first beam can further carry a coupling member for connecting the trailer to a pulling vehicle.

In this application the term ‘trailer’ is otherwise understood to mean any vehicle pulled by another vehicle, regardless of the manner in which the pulling vehicle and the pulled vehicle are connected to each other.

In an embodiment of the beam an upper side of the first beam can be configured at least at the position of or close to the free end part to carry a load. The load resulting from the cargo is hereby transmitted directly into the beam, enabling it to deform and enabling the load to drop down closer toward the road surface.

In another embodiment at least one of the upper side and an underside of the first beam can be chamfered and/or curved, at least at the position of or close to the free end part, in the direction of the other of the upper side and the underside thereof. A chamfered or curved progression of the upper and/or underside enables the decrease in height and the associated increase in the formation to be realized gradually. When the upper side of the first beam is chamfered or curved, the progression of this upper side can be adapted to a local contour of the load to be transported.

The at least one chamfered and/or curved side can here extend over at least 25%, preferably at least 50%, and more preferably at least 75% of a length of the beam, calculated from the free end part to the connecting part. The further the chamfered and/or curved part of the beam extends, the greater the deformation in particular can be.

In a variant of this embodiment the at least one chamfered and/or curved side can even extend over substantially the whole length of the beam.

On the other side, the upper side of the first beam can in this embodiment be substantially parallel to the underside thereof close to the connecting part. This causes the form of this connecting part to correspond with that of the second beam, so that both the upper side and the underside of the connecting part can form a slide bearing with internal surfaces of the second beam.

In another embodiment of the girder the dimension of the first beam in the height direction at the position of or close to the free end part can amount to at most 80%, preferably at most 65% and more preferably at most 50% of the dimension in height direction at the position of or close to the connecting part. The smaller the height of the first beam close to its free end part, the greater the available additional space and the bending.

In a further embodiment the second beam can be received slidably in at least one subsequent beam, the dimensions of which are larger in cross-sectional direction than those of the second beam. A telescopically extendable girder with more than two beams, which is suitable for trailers having to provide a high degree of extension, can thus be formed. The invention further relates to a sliding beam for use in a girder as described above. Such a sliding beam can comprise a connecting part to be enclosed in a surrounding beam and a free end part located opposite, wherein a dimension of the sliding beam in the height direction is smaller at the position of or close to the free end part than at the position of or close to the connecting part.

Finally, the invention relates to a trailer comprising a chassis with at least one axle and a girder as described above, extending from the chassis. As a result of the additional space which is created by the reduced height of the front beam, in combination with the additional bending thereof, such a trailer is suitable for transport of loads having their greatest height at the front side of the girder. As stated above, the most well-known example of such a load is a rotor blade of a wind turbine, the root of which is the thickest (so in lying transport the highest) part.

In an embodiment the trailer can be a semi-trailer and the free end part of the first beam can be connected to a gooseneck.

The invention is now elucidated on the basis of an embodiment, wherein reference is made to the accompanying drawing, in which:

Fig. 1 is a partially transparent side view of a combination of a pulling vehicle and a trailer which is provided with a girder according to the invention, wherein the girder is shown in extended situation, loaded with a load, while the first beam is located on the ground,

Fig. 2 is a view corresponding with Fig. 1 of the pulling vehicle-trailer combination of Fig. 1 in roadworthy situation, wherein the gooseneck and the chassis have been moved upward,

Fig. 3 is a detail view on enlarged scale of the pulling vehicle and the front part of the trailer in the situation according to Fig. 2,

Fig. 4 is a schematic front view of the trailer of Fig. 1-3, wherein the size of the spaces between the successive beams is exaggerated, and

Fig. 5 is a schematic side view of the first beam of the girder according to the invention, wherein the size of the dimensions in height direction is exaggerated.

A trailer 1 comprises a chassis 2 with, in the shown embodiment, four axles 3 and a telescopically extendable girder 4 extending from the chassis 2 (Fig. 1, 2). In the shown embodiment trailer 1 is a semi-trailer and the girder 4 is connected on its front side via a coupling piece 25 to a gooseneck 5. In this embodiment this gooseneck 5 is connected to a separate chassis 6 with two axles 7, a so-called low loader dolly. This low loader dolly is in turn connected via a rotating dish 8 to a pulling vehicle or truck 9, this having four axles 10 here.

Girder 4 comprises a first beam 11 with relatively small dimensions in cross-sectional direction, which is received slidably in a second beam 12 with relatively larger dimensions in cross-sectional direction (Fig. 4). In the shown embodiment the second beam 12 is in turn received slidably in a third beam 13, the dimensions of which are larger again in cross-sectional direction than those of second beam 12. This third beam 13 is received slidably in a larger fourth beam 14, which in turn is received slidably in an even larger fifth beam 15. This latter beam 15 here forms part of the chassis 2, a deck 29 and braces 30 of which are shown schematically. The beams 11-15 each have a closed cross-sectional form here.

Girder 4 has an underside 16 which is directed toward a ground surface or road surface 17 when girder 4 is installed in trailer 1. Girder 4 further has an upper side 18 lying opposite the underside 16. Together, underside 16 and upper side 18 determine a height direction H of girder 4.

First beam 11 of girder 4 comprises a connecting part 19 (also referred to as overlapping part) which is enclosed in the second beam 12, and a free end part 20 located opposite (Fig. 3). According to the invention, a dimension hi of the first beam 11 in the height direction at the position of or close to the free end part 20 is smaller than a corresponding dimension hi in height direction at the position of or close to the connecting part 19 (Fig. 5).

This smaller height hi of the free end part 20 can be achieved by giving upper side 27 and/or underside 28 of first beam I l a chamfered and/or curved form. The chamfering or curvature can be limited to the vicinity of the free end part 20 but can also extend over a greater part of a length L, calculated from free end part 20 to connecting part 19 of first beam 11, for instance over at least 25%, at least 50% or at least 75% of the length L. In the shown embodiment the upper side

27 is chamfered over the whole length of first beam 11, which thus causes this beam to taper as seen in height direction. It is however also possible to envisage a segment 27H of upper side 27 being parallel to underside 28, at least at the position of connecting part 19, as shown schematically in Fig. 5 with a dot-dash line. In this way first beam 11 can be guided by the parallel surfaces 27H,

28 while sliding in and out in second beam 12.

The smaller height hi of free end part 20 of first beam 11 results directly in additional space Ahi above the front part of girder 4. This additional space Ahi can for instance amount to 20%, 35% or even 50% of the height dimension hi at the position of connecting part 19. In addition, the smaller height results in a lower bending stiffness, whereby the first beam 11 of girder 4 bends under load to relatively greater extent than the other beams 12-15. This also creates additional space Ahj, as shown schematically on exaggerated scale by the broken lines Du and DL and in Fig. 5.

Owing to this additional space a rotor blade 21 will protrude less high above road surface 17 when it is loaded on trailer 1 than in the case of the known trailer according to US 2011/187083 Al. This enables road transport of rotor blade 21, also when there are obstacles above the road, such as overpasses or bridges, along the route. Rotor blade 21 is here carried with its root 22 and the part connecting thereto by first beam 11 of girder 4, while rotor blade 21 is carried close to its outer end or tip 23 by a support 24 which can be mounted on the chassis 2 of trailer 1.

As shown by a comparison of Fig. 1 and Fig. 2, first beam 11 bends when gooseneck 5 with girder 4 thereon is moved upward. First beam 11 here takes on to some extent the form of the contour of the part of blade 1 close to root 22 resting thereon. Moving gooseneck 5 upward is otherwise done in known manner by a hydraulic lift system (not shown here) incorporated therein. The travelling height of chassis 4 is here adjusted by means of the air suspension such that blade tip 23 does not protrude any higher above road surface 17 than blade root 22.

Although the upper side 27 of first beam 11 is shown as chamfered in the shown embodiment, it will be apparent that the different in height between connecting part 19 and free end part 20 could also be achieved with a different form. The upper side 27 could for instance be curved (concave or convex), or could consist of a plurality of segments with different degrees of chamfering or curvature. The upper side 27 could also be straight, and the underside 28 could conversely be chamfered or curved. It is also possible for both sides 27, 28 of first beam 11 to be chamfered and/or curved.

The remaining beams 12-15 are prismatic here, and so have a constant height dimension over their whole length.

In practice however, the beams 11-15 forming a telescopically extendable girder for a trailer are not perfectly straight, but are all curved upward with a great radius of curvature in the order of 150-800 metres. This is because, in extended situation of girder 4, the beams 11-15 will bend under the influence of their own weight. By giving beams 11-15 an upward curvature, i.e. biasing them, this bending is compensated for and girder 4 will have a substantially constant distance to road surface 17 over its whole length in extended state. In the shown embodiment the beams 11-15 each have a length of about 16 metres, wherein in extended state the overlapping part between the end edges 31, 32 amounts to about 10% of this length. With such lengths the maximum bending in the centre of girder 4 can amount to more than 1 metre. This is then the distance which is compensated by a suitably chosen curvature or bias.

The invention thus enables road transport of a load, the highest part of which is located on the front side in the direction of travel, also in the event that the route passes obstacles such as overpasses and bridges arranged over the road.

Although the invention is elucidated above on the basis of an embodiment, it will be apparent that it can be varied in many ways. The scope of the invention is defined solely by the following claims.