Off-road lift trucks with telescopic arms are known in the prior art, recently going by the name of "telehandlers"; they are equipped with box sections, usually rectangular in shape.

In consideration of the types of stress these arms are subject to, rather different to those crane arms are designed to withstand, the sections have a degree of resistance to flexion which is not entirely satisfactory, as they exhibit problems of instability due to buckling as well as instability to lateral solicitations.

Document FR-A-2790538 discloses a telescopic arm with a rectangular beam structure comprising: a flat top; two upper curved angles directing downwards; two sides; two lower curved angles extending from the sides; and a bottom. The sides extend downwards from the upper angles, and have a fold with the edge directing outwards and placed under the medium axis. The bottom lower angles also have a fold with an edge directing outwards and placed on a vertical axis. The telesscopic arm having at least one extrernal arm and at least one extending arm which is slidably inserted along a longitudinal axis thereof internally of the external arm and is complementary shaped in relation to the external arm. Sliding elements are interposed between the external arm and the extending arm and comprise a support , solidly constrained to the external arm and a skate, solidly constrained to the support. The sliding elements are fixed and not adjustable in a simple way in order to enable manufacturing errors in the various components to be corrected and to allow take up to compensate for wear and other deformations.

The main aim of the present invention is to obviate the last above-mentioned drawbacks in the prior art.

A further aim of the invention is to realise a system of skates for relative sliding of the arms, which is easy to mount, dismount and adjust.

An advantage of the invention is that it is simple.

A further advantage of the invention is that is improves resistance to buckling of the lower side, which is subject to compression, of the box section of the arms, in comparison to a traditional rectangular section of a same area.

A further advantage of the present invention is due to the special shape of the section of the arms by virtue of which the extending arm couples, under the effect of the load, with the external arm, creating a sort of wedge effect that increases guidability and the precision of the coupling between the two arms. In this way, in the case of lateral solicitations, the telescopic arm is very stable thanks to a self-centring action of the coupled arms. There is also an automatic take-up of play in the coupling between the external arm and the extending arm.

Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of some embodiments of the device, illustrated purely by way of a non-limiting examples in the accompanying figures, in which:

• figure 1 illustrates a straight transversal section made according to a plane which is perpendicular to the longitudinal axis of the telescopic arm;
• figure 2 is the same section as in figure 1, relating to a further embodiment of the invention.

With reference to the figures of the drawings, the telescopic arm (for a lift truck) of the invention comprises at least an external arm 2 and at least an extending arm 3 which is slidably inserted along a longitudinal axis x (perpendicular to the plane of the drawing) internally of the external arm 2 and is complementarily shaped with respect to the external arm 2. The external arm 2 and the extending arm 3 have box sections in which a lower part 4 exhibits at least two tracts 5, symmetrically arranged with respect to a vertical plane of symmetry π (containing the longitudinal axis x) which at least two tracts 5 delimit a concavity facing internally of the section and are inclined by a determined angle of inclination α with respect to the plane of symmetry π. Preferably the angle of inclination α is comprised between 60° and 89°.

In a first embodiment the two tracts 5 are joined at the vertical plane of symmetry π. The lower part of the box section of the external arm 2 and the extending arm 3 exhibits a V-shape with the vertex thereof facing externally of the section.

In a second embodiment, the two tracts 5 are conjoined by a straight tract 5a which is perpendicular to the plane of symmetry π.

Sliding elements 6 are located between the external arm 2 and the extending arm 3, which sliding elements 6 are arranged longitudinally at comers of the extending arm 3 and are complementarily shaped to the comers. Preferably the sliding elements 6 do not extend over the whole length of the comers, but are subdivided into a plurality of tracts of shorter length aligned along the comer. Each of the sliding elements 6 comprises a support 7, solidly constrained to the external arm 2, and a skate 8, solidly constrained to the support 7, arranged in contact with the external surface of the extending arm 3. Each of the skates 8 comprises at least two portions 8a, 8b which are not joined and which are arranged respectively in contact with two adjacent faces of the extending arm 3. The two portions 8a, 8b are connected to the respective support 7 by removable or unremovable means for connection, preferably screws or pins. The two portions 8a and 8b of each skate 8 are non-joined at a plane which is parallel to the longitudinal axis x and which passes in proximity of the corner at which the skate 8 is located. This means that the skate can adapt to the shape of the extending arm 3 without fracturing or cracking at the internal vertex, as happens with skates currently in use in the prior art.

Each support 7 is solidly constrained to the external arm 2 by adjustable means for connecting which enable an adjustment of the position of the relative sliding element 6 along at least two directions which are perpendicular to the faces of the external arm 2; the adjustable means for connecting join up to each other at the corner the sliding element 6 is situated on.

The adjustable means for connecting comprise a plurality of screws 9 which pass through the breadth of the external arm 2, through respective slots, and are arranged with longitudinal axes thereof perpendicular to respective faces of the external arm 2. The screws 9 are solidly constrained at one end thereof to a respective support 7, while at the other end thereof they are provided with a nut 9a which is predisposed to be tightened externally in contact with the external arm 2. The adjustable means for connecting, as described above, enable each skate 8 to be arranged in contact with the extending arm 3, in order to compensate any errors in shape and size of the extending arm 3. Each screw can translate parallel to itself along the slot in which it is arranged, following displacements imposed by the other screws, so that each skate 8 can be fixed in a determined position in contact with the extending arm 3.

Making each skate 8 in two portions leads to considerable production advantages (reduction in waste and working times) and means that the two portions can be assembled separately on a corresponding rigid support at a distance of a few millimetres from one another, enabling manufacturing errors in the various components to be corrected (it is possible that considerable tolerances were allowed during manufacture of the parts), and allowing take-up to compensate for wear and any other deformations.

There is a further advantage which consists in the fact that each portion of skate (or half-skate) is completely independent as regards adjustment and for take-up of play, and can also be replaced independently of the contiguous portion, with evident savings.

Overall the shape of the section of the arms and the independent adjustment of the skates make the coupling between the external arm and the extending arm extremely precise and stable, and improve the rigidity and characteristics of guidability thereof.