The invention concerns a frame for a vehicle, which frame contains at least two longitudinal members and at least one wheel shaft supported on bearings which are fixed to these longitudinal members.

By vehicle is meant a drawn vehicle as well as a self- driving vehicle, both with at least one shaft on both ends as with at least one shaft on the rear end only.

In particular, the invention concerns, however not exclusively, a trailer with one or more shafts on the rear end.

With such frames, the longitudinal members are made of metal, usually steel.

Longitudinal members of steel are relatively heavy, as a result of which also the frame is relatively heavy.

That is why frames with longitudinal members made of aluminium are already used. They are lighter but relatively expensive. In order to offer the same bending strength and torsional strength as steel, aluminium struts must have a larger section.

The invention aims a frame which does not have these and other disadvantages, and which thus has a larger strength, but is nevertheless relatively light and inexpensive.

This aim is reached according to the invention in that the longitudinal members are made of composite material.

Members made of composite material - i.e. synthetic material reinforced with fibres - are known as such, but they have not been applied yet in frames.

In particular, the longitudinal members are pultruded members.

In the case where the members of the wheel shaft or wheel shafts are connected to a longitudinal member in a springy manner and in particular by means of a connecting piece, what is called a trestle, said trestle will be glued to the longitudinal member according to a particular embodiment of the invention.

Practically, the longitudinal members are composed members containing two base struts with a U-shaped section which are directed with their cores to one another and which are connected to one another by at least two smaller connecting struts, in particular U- struts, which are glued with their legs to the cores of the above-mentioned base struts.

The above-mentioned trestles can then be provided with one part between the two base struts, possibly where there is an interruption of one or more connecting struts between said base struts, and they can be glued to both base struts.

Preferably, also the trestles are made of composite material.

The frame may also contain one or several cross members

between the longitudinal members, whereby these cross members are also mainly made of composite material, for example by applying the filament winding process.

In order to better explain the characteristics of the invention, the following preferred embodiment of a frame according to the invention is described as an example only without being limitative in any way, with reference to the accompanying drawings, in which:

figure 1 shows a lorry with a trailer according to the invention; figure 2 shows the part which is indicated by F2 in figure 1 to a larger scale; figure 3 shows the section according to line III-III in figure 2 in perspective; figure 4 shows a view according to F4 in figure 3; figure 5 shows a section according to line V-V in figure 3; figure 6 shows a side view of a part of a trailer analogous to that in figure 2, but with reference to another embodiment thereof; figure 7 shows a section according to line VII-VII in figure 6; figure 8 shows a section according to line VIII-VIII in figure 7; figure 9 shows a section analogous to that in figure

8, but with reference to another embodiment; figure 10 shows a section according to line X-X in figure 1 to a larger scale.

Figure 1 shows a combination of a lorry 1 with a trailer 2, whereby the trailer 2 as usual consists of a frame 3 resting on two wheel sets at the back and upon which is

provided a floor 4 or superstructure.

These wheel sets, as is represented in detail in figure 2, hereby mainly consist of a wheel shaft 5 supported on bearings 6 which are connected to the frame 3 in a springy manner and of wheels 7 fixed on the ends of the wheel shaft 5.

The frame 3 mainly consists of two composed longitudinal members 8 and of cross members 9 mounted in between them.

The longitudinal members 8 are composed of two base struts 10 with a U-shaped section and two smaller connecting struts 11 which also have a U-shaped section, whereby both the base struts 10 and the connecting struts 11 are pultruded struts or struts made by means of pultrusion from composite material. Composite material is synthetic material reinforced with fibres, such as polyester reinforced with glass fibre. Also other synthetic materials or polymers can be used. Instead of glass fibres, other reinforcement fibres can be used such as carbon fibres, aramid fibres and such.

By pultrusion is meant a method known as such whereby a reinforcement formed of fibres or a tissue is moisturized with synthetic material by means of immersion or spraying, and whereby the soaked fibres or the soaked tissue are subsequently pulled through a heated extrusion device, after which the synthetic material cures.

As is represented in figures 3 and 5, the base struts 10 with their vertically erected cores are directed towards one another, with a distance between said cores. As a result, the legs are pointed laterally outward.

The connecting struts 11 are situated with their cores on top of and at the bottom of the base struts 10 respectively, and thus with their legs pointing towards one another.

The legs of these connecting struts 11 are glued to the backsides of the cores of the base struts 10, for example by means of a two-component glue such as epoxy.

The springy mounting of each layer 6 in relation to a longitudinal member 8 is carried out, as is represented in detail in figure 2, by means of a securing element, what is called a trestle 12, which is situated with its top part between the two base struts 10 of the longitudinal member 8, at the height of an interruption 13 of the connecting struts 11.

Said trestle 12 has the shape of a tube which reaches to the top side of the longitudinal member 8 and which, under said longitudinal member 8, is bevelled on the back side.

The end of the trestle 12 situated between the base struts 10 is glued to the cores of these base struts with two flat side walls.

A glue is selected which is similar to the glue used for composing the longitudinal members 8.

Under the longitudinal member 8, the trestle 12 may possibly widen somewhat to prevent the base struts 10 from shifting downwards with slightly protruding parts.

Right through the two base struts 10 and the trestle 12

may possibly be provided a bolt 14 upon which is screwed a nut 15. This bolt 14 is provided in a neutral place where there is no relative movement of the surfaces of the base strut 10 and the trestle 12 which are situated against one another, and where the forces on the base struts 10 are minimal.

This bolt 14 does not serve to absorb forces, but it helps to prevent a lateral shift of the trestle 12 in relation to the two base struts 10. Moreover, the bolt 14 keeps the trestle 12 and the base struts 10 together, such that they cannot move during the curing of the glue.

The trestle 12 can be made of steel or aluminium, but it is preferably also made of composite material, for example by moulding it under pressure and heat, by means of what is called compressing moulding or the hand lay-up method. The compressing moulding technique consists in putting the polymer and the reinforcement fibres or a mat of pre-impregnated fibres in a heated mould, and by subsequently pressing the mixture of polymer and reinforcement in the required shape under a large pressure of for example some 100 tons per m ² .

At the lower end of the trestle 12 is fixed a leaf spring 16, possibly by means of hinges. At a distance from the trestle 12, the bearing 6 is fixed on the leaf spring 16 by means of fasteners 17.

Between the bearing 6 and a part of the trestle 12 situated under the longitudinal member 8 is provided a shock absorber 18, whereas bellows 19 are situated between the free end of the leaf spring 16 and the longitudinal member 8 which are connected to a compressed

air source in a manner which is not represented in the figures.

If necessary, the longitudinal members 8 can be reinforced at the bottom near the wheel shafts 5 by means of auxiliary longitudinal members 20, as is represented in figures 6 to 8.

These auxiliary longitudinal members 20 have the same section and are manufactured in the same manner as the longitudinal members 8. Only their length is much shorter.

The longitudinal members 8 and 20 are situated right underneath one another. The trestles 12 which are fixed to the longitudinal members 8 extend between the two base struts 10 of the auxiliary longitudinal member 20 and are glued to these base struts 10 in the same manner as they are to the longitudinal members 8. The bellows 19 are erected between the leaf spring 16 and the auxiliary longitudinal member 20.

The cross members 9 each consist of a round, tubular body 21 and round flanges 22 on both ends as represented in figures 5, 7 and 8. The body 21 is made of composite material, in particular by means of pulwinding or filament winding.

Pulwinding is a variant of pultrusion, whereby one or several layers of reinforcement fibres are wound on a mandrel and are soaked with polymer prior to and/or after the application, after which the whole is pulled through an extrusion part, after which the polymer cures.

Filament winding is a method whereby reinforcement fibres or ribbons soaked with polymer are wound on a rotating mandrel or cylinder, after which the polymer cures.

The flanges 22 are made as separate from composite material, preferably by means of the above-mentioned compressing moulding technique, and they are glued to the ends of the body 21, preferably by means of a two- component glue such as epoxy. The connection of the flanges 22 to the body 21 is rounded on the side which is turned away from the end by means of a synthetic material such as polyester.

The cross members 9 are glued with their flanges 22 to the core of a base strut 10 of the two longitudinal members 8 and/or of the two auxiliary longitudinal members 20 by means of a flexible glue, for example a two-component glue.

In order to absorb shearing forces and to maintain the flanges 22 in place during the curing of the glue, it is possible to further fix each of the flanges 22 to the cores of the base struts 10 by means of four bolts 23 and nuts 24.

If a cross member 9 is provided between the longitudinal members 8 at the height of two trestles 12, the bolts 23 may replace the above-mentioned bolt 14.

Also between the parts of two trestles 12 situated opposite one another which protrude at the bottom may be provided a cross member 9 in the above-described manner, as is represented in figures 6 and 7.

The obtained tubular construction of the composed longitudinal members 8 provides a particular torsional strength. Thanks to the composite material and the gluing of the struts 10 and 11, these members are particularly strong and light.

The cross members 9 do not only keep the two longitudinal members 8 in place, but also absorb the torques of the frame 3 in the longitudinal direction. The above- described cross members 9 are particularly fit for this.

The top side of the trestle 12 being situated between the base struts 10 of a longitudinal member 8, makes it possible for this trestle 12 to be glued with two vertical side walls and on both sides to the two base struts 10, which results in a very large contact surface and prevents a load in one particular point on the longitudinal member 8.

All this allows for a significantly better connection of the trestle 12 to the longitudinal member 8 than a plate which is fixed at the end of the trestle 12 and which would be fixed to the bottom side of the longitudinal member 8 by means of glue, bolts or a combination thereof. Tests have proven that the latter mounting of the trestle 12 results in the connection being torn after a while.

Not only the longitudinal members 8 are very strong and light, but also the springy connection of the trestles 12 is particularly strong. Partly thanks to this strong connection, it has become possible to use composite material for the struts 10 and 11.

The above-mentioned cross members 9 must not necessarily be provided with flanges 22 at their ends.

They can be made according to another embodiment as represented in figure 9, whereby their tubular body 21 is provided with a thickening 25 on both ends. This thickened end has a sufficiently large surface to be glued tightly to the longitudinal members 8, either or not with additional bolts.

According to this embodiment, the body 21 is obtained by means of pulwinding or filament winding.

At the front, the above-described trailer 2 may contain, as is represented in figure 10, a plate 26 made of composite material which is glued to the bottom side of the two longitudinal members 8 and which carries a king pin 27 at the bottom with which the trailer 2 can be connected to the pivoting platform 28 of the lorry 1.

The invention is by no means limited to the embodiment described above and represented in the accompanying drawings; on the contrary, such a frame can be made in all sorts of variants while still remaining within the scope of the invention.