The invention relates to a fuel tank or secondary fluid tank, consisting of thermoplastic, for a motor vehicle, with a non-rotational symmetrical geometry. Such non- rotationally symmetrical geometries are usually not internal-pressure optimized, that is to say that boiler formulae are not applicable to these when calculating the pressure resistance.

Especially in the case of fuel tanks consisting of thermoplastic but also in the case of other operating fluid tanks or secondary fluid tanks for motor vehicles it is desirable to design these to be essentially dimensionally stable against the occurrence of internal pressure/overpressure, for example, in the tank in relation to atmospheric pressure. Such tanks, as regards their shape, are frequently adapted to the installation situation in the motor vehicle so that it is often not possible to design the tank in a correspondingly pressure-resistant manner due to the external contour. By their geometry, cylindrical or spherical tanks are suitable for absorbing an increased internal pressure, as is generally known. Such a design of fuel tanks, operating fluid tanks or other secondary fluid tanks, such as oil tanks, windscreen wash tanks, urea tanks or the like is usually not possible owing to the limited available installation space in a motor vehicle.

Particularly in the case of fuel tanks consisting of thermoplastic, it is known and desirable to structurally partially stiffen these in order to ensure a certain volume constancy of the tank during pressure fluctuations in order to avoid sagging of large-area wall sections in the case of larger completely filled tanks and in order to avoid creeping of the plastic during long-term internal pressurization . Moreover, butting of the plastic fuel tank against the body of the motor vehicle is to be avoided. These previously described measures attend essentially to various problems which to a greater or lesser extent are concerned with the lower material strength of the plastic compared with metal, for example, and with the creep tendency of specific thermoplastics.

Fuel tanks, especially for diesel fuels, are usually designed as non-pressurized systems so that the dimensional stability of the plastic in relation to internal pressure-induced deformation hardly plays a role. In the case of hybrid vehicles with Otto engines, however, the pressure resistance of the fuel tank increases in importance since with such tank systems it is desirable to hermetically seal these in relation to atmosphere over longer time periods. The necessity to hermetically seal the tank results from the fact that the internal combustion engine compared with conventional Otto engines has fewer or shorter operating cycles so that fewer or shorter backflushing cycles are made available for the fuel vapor filter of the fuel tank. Consequently, either the capacity of the fuel vapor filter has to be increased significantly or the tank has to be hermetically locked during non- running periods of the vehicle, for example. Apart from these special problems, it is naturally desirable to install altogether smaller fuel vapor filters.

Pillar-like supports or tie rods, for example, which are provided in the tank and support or fix the large- area wall sections of the tank in relation to each other, are known as structure reinforcing measures on fuel tanks. It is also known to introduce metal structures into the tank wall. Finally, it is known to stiffen the tank in sections with so-called organo sheets, which is comparatively time-consuming and expensive.

Tanks consisting of plastic are frequently secured on the supporting structure of the vehicle by means of metal clamping straps, wherein these measures only have the effect of supporting the tank and prevent sagging of larger wall sections of the tank but do not actually reinforce or stiffen the structure of the tank.

The invention is therefore based on the object of developing a plastic tank, as an operating fluid tank for a motor vehicle, especially a secondary fluid tank or fuel tank, in such a way that this is structurally reinforced against internal pressure-induced deformation using the simplest possible means. Such a reinforcement is to be applied particularly easily, without being bulky, and to be inexpensive.

The object upon which the invention is based is achieved by means of a fuel tank or secondary fluid tank, consisting of thermoplastic, for a motor vehicle, with a non-rotationally symmetrical geometry, wherein the outer skin of the tank is provided with at least one tension-resistant strap, wherein the strap spans the tank and/or is fastened between at least two anchor points which are provided at a distance from each other on the outer skin of the tank, wherein the strap comprises an arrangement of tension-resistant fibers, which tension-resistant fibers are embedded into a thermoplastic or duroplastic matrix and the strap is welded and/or adhesively fastened to the outer skin of the tank at least in the region of the anchor points. Predetermined points or regions on the outer skin of the tank are regarded as anchor points within the sense of the invention, the predetermined points or regions being provided at least as fixing points for the strap which is to be welded to the outer skin of the tank, i.e. the strap is welded to the outer skin of the tank at least in these regions.

The strap, as a longitudinal fiber-reinforced thermoplastic strap, can be completely or partially connected in a materially bonding manner to the outer skin of the tank, i.e. be welded. The strap can encompass the tank by its full extent or be applied only in strips on specific wall sections of the tank. Both in the case of the strap encompassing the tank by its full and in the case of the strap being applied only in strips on specific wall sections of the tank, this strap can be laid or applied in a crosswise manner .

Apart from the fact that such a strap which is welded to the outer skin of the tank achieves a slight increase of the surface bending moment of the tank wall, the welding of the strap between anchor points on the tank especially has the effect of large-area wall sections of the tank between the anchor points being virtually bridged so that in the event of a possible bulging of the tank the tensile forces which are introduced into the strap are directed into the anchor points of the tank.

The knowledge is based on the fact that in the case of a non-rotationally symmetrical tank geometry different sections of the tank wall have various degrees of stiffness. Particularly the corner regions of the tank, or of wall-to-wall welds, so-called "kissing points", or other projections in the tank geometry are structurally stiffer than large-area smooth-walled sections of the fuel tank. Since the strap, at least in the region of the anchor points, is preferably also connected in a materially bonding manner over its entire length to the outer skin of the tank, relative movements between the strap and the tank wall cannot occur, which represents the significant difference to a simple encompassing of the tank with a clamping strap which is not connected to the tank in a materially bonding manner.

The strap preferably extends rectilinearly between at least two anchor points so that this directly absorbs tensile forces in the event of internal pressure- induced occurrent deformation of the tank wall. The strap can extend in this case either in sections, projecting from the tank wall, rectilinearly between two or more anchor points, but can also be arranged in at least one groove or strap channel of the tank which is provided in the outer skin.

The tank can be adapted in an altogether geometrically comparatively simple manner to the position of a strap or of a plurality of straps. This can have a strap channel, or a plurality of possibly even crossing strap channels, for accommodating straps.

Structurally stiffer sections of the tank wall, for example corners or corner regions of the tank wall, are expediently provided as anchor points.

The strap expediently extends between at least two anchor points which form structurally stiffer sections of the tank geometry, and in the process bridge and/or encompass comparatively less stiff sections of the tank geometry between the anchor points.

In an advantageous variant of the tank according to the invention, it is provided that means for structural stiffening of the tank wall are additionally provided at least in the region of the anchor points of the strap or of the tank. For example, suitable profilings of the tank wall, reinforcing inserts, for example consisting of metal, which are integrated into the tank wall, or supports/tie rods or the like provided in the interior of the tank, can be provided as such additional means for the structural stiffening of the tank wall.

The tank wall can be provided for example at least in sections with grooves and/or ribs which extend parallel to each other, wherein the strap expediently fits over the ribs and for example on the outwardly projecting ribs in the region of abutment against the ribs is welded to these. The ribs and/or grooves can have different or the same cross sectional profiles.

In a preferred variant of the tank according to the invention, at least two anchor points are provided at a distance from each other in the corner regions of the tank geometry, or are arranged so that the strap spans at least one corner region of the tank structure. A large-area side of the tank can be provided for example with two straps which are seated in each case in the corner region of the tank structure and cross over roughly at the area center of gravity of the tank wall in question, which straps are welded to the tank wall either only in the corner region or over their entire length. For example, two anchor points can be provided in the region of the support of a tank wall by means of structure-reinforcing elements in the interior of the tank or in the tank wall.

The strap advantageously supports large-area tank walls between structurally stiffer tank wall geometries against bulging and/or sagging. One variant of the tank according to the invention is distinguished by fastening structures for the body connection, wherein the fastening structures form anchor points for the strap. Fastening plates or fastening angle brackets, for example, which are formed in one piece and preferably encompassed by one strap or by a plurality of straps can be provided as fastening structures. The strap is expediently provided as a so-called "prepreg strap" which comprises glass fibers or carbon fibers or aramide fibers or basalt fibers in a thermoplastic matrix based on polyethylene. The fibers can alternatively be embedded into a duroplastic matrix, for example on an epoxy resin base. The glass fibers, carbon fibers, aramide fibers or basalt fibers are expediently formed as endless fibers.

The object upon which the invention is based is also achieved by means of a method for producing a fuel tank or secondary fluid tank for a motor vehicle by producing a non-rotationally symmetrical hollow body consisting of thermoplastic, wherein at least one tension-resistant strap with tension-resistant fibers in a thermoplastic or duroplastic matrix is applied to the outer skin of the hollow body so that this spans the tank or extends between structurally and/or geometrically stiffer sections of the tank, wherein the tank, at least in the region of the stiffer sections of the tank, is welded and/or adhesively fastened to the outer skin of tank at predetermined anchor points of the outer skin of the tank, wherein the strap is arranged on the outer skin of the tank so that this absorbs tensile forces in the event of internal pressure-induced deformation.

The tank according to the invention can be produced by means of extrusion-blow molding, for example, wherein the strap is welded to the tank preferably after the forming of this.

The welding can be carried out for example by fusing and pressing a prefabricated strap, for example a so- called "prepreg strap", onto the outer skin of the tank .

The strap can be welded by means of a laser, infrared radiation or hot air, for example.

For this purpose, it can be provided, for example, to clamp the tank in a rotating device and to unwind a strap from the roll. During the winding off process, the strap, for example in the region of its abutment against the tank, can be softened or fused by means of a laser and pressed onto the outer skin of the tank using a press-on roller.

In a preferred variant of the method according to the invention, it is provided that the strap is welded over its entire contact surface or over its entire length to the outer skin of the tank. Such an attachment of the strap onto the outer skin of the tank has the advantage that for example by means of the strap flat reinforcing elements or insulation mats can be fixed on the outer skin of the tank. If the reinforcing elements also comprise at least one outer layer of thermoplastic material, the strap can also be welded to this right across the reinforcing elements.

The strap according to the invention can be in a single layer or multilayered, for example, in the region of thin points of the tank wall in order to be wound around this or to be applied to this. The strap can, for example, also fit over functional components which are provided on the tank on the outside or lines which are laid there so that these are fixed by means of the strap .

The fixing points or anchor points on the outer skin of the tank serve virtually as locating bearings between which the strap can transmit tensile forces. In this case, for simplicity the corner regions or structurally stiffer regions of the tank geometry are considered to be virtually stiff. By means of the strap or by means of a plurality of straps so-called organo sheets can also be fixed on the outer skin of the tank, for example.

The invention is explained below based on exemplary embodiments which are represented in the drawings.

In the drawing:

Figure 1 shows a perspective view of a tank according to the invention with a strap which is partially attached to the outer skin of the tank, specifically during the attaching of the strap,

Figure 2 - shows a sectional view along the lines I - I in Figure 1,

Figure 3 shows a cross section through the tank along the lines III - III, Figure 4 shows a view of the details IV in Figure 3,

Figure 5 shows a view of the detail V in _. Figure 3,

Figure 6 shows a perspective view of a further exemplary embodiment of the tank according to the invention,

Figure 7 shows a perspective view of a third exemplary embodiment of the tank according to the invention,

Figure 8 shows a cross section through the tank according to Figure 7, Figure 9 shows a cross-sectional view of a fourth exemplary embodiment of the tank according to the invention,

Figure 10 shows a schematic representation of a tank wall which is reinforced in sections and is encompassed by two straps.

The tank 1 according to the invention can be designed as a fuel tank for a motor vehicle, for example. This is shown in greatly simplified form in the figures, just as the geometry/contour of the tank 1 is simplified .

The tank 1 comprises tank walls 2 consisting of thermoplastic based on HDPE (high density polyethylene) and was obtained for example by means of extrusion-blow molding or injection molding from thermoplastic. The tank walls 2 can consist of a laminated extrudate or co-extrudate consisting of thermoplastic, for example.

The tank 1 which is shown in Figure 1 has an approximately cubic geometry, wherein this has larger side walls 3 and smaller end walls 4 and also edges 5 which delimit the side walls and end walls.

In the case of the variant of the tank 1 according to the invention shown in Figure 1, it is provided that the outer skin of the tank 1, i.e. the outwardly pointing surfaces of the tank walls and side walls, are encompassed by a strap 6 which, for example, is connected over its entire length in a materially- bonding manner to the outer skin of the tank 1. The strap 6 comprises, for example, tension-resistant fibers, oriented in its longitudinal direction, in the form of carbon fibers, aramide fibers or glass fibers, which are embedded into a thermoplastic matrix.

The strap 6 is prefabricated as a so-called "prepreg strap" and is welded to the outer skin of the tank 1 after the forming of said tank 1. For this purpose, the strap 6 from a roll 7 is laid flat on the outer skin of the tank 1, is locally heated and fused during application by means of infrared radiation, laser radiation or hot air, for example, in the region of the abutment against the outer skin of the tank 1, and by means of a press-on unit, which is not shown, is pressed with a press-on roller, for example, against the tank walls 2, 3, 4 in the region of the softened point so that on account of the pressure which is applied in the region of the contact line welding of the strap 6 to the tank wall 2, 3, 4 is carried out.

In the case of the variant of the tank 1 shown in Figure 1, the strap 6, as already mentioned in the introduction, is welded to the outer skin of the tank 1 over its entire length, but a weld can be provided at just a few points of the outer skin, which are subsequently referred to as anchor points 10.

Such anchor points 10 can be sections of the tank walls 2 which either directly adjoin edges 5 or corners 8 of the tank walls 2 or are formed by the corners 8 or edges 5 themselves.

In Figure 1, in the side wall 3 of the tank facing the viewer, provision is made for a recess 9, the position and arrangement of which in the described exemplary embodiment serves only for reasons of illustration.

The recess 9 is spanned by the strap 6, wherein the strap 6 itself is laid in a channel 11, which is formed as a groove, provided in the tank 1.

Also for reasons of illustration, in Figure 3 the strap 6 is shown spanning the recess 9 at a distance. The effect of the strap 6 which is referred to in the introduction is now provided when the strap 6 extends at least between the anchor points rectilinearly over the tank wall 2 in question. A favorable extent of the strap 6 over one side wall, or over a plurality of side walls 3, of the tank 1 may result for example if the strap 6, differing from the view in Figure 1, were to extend diagonally over the side wall 3 in question and were to be welded to the tank in the corners 8 or behind the corners of said tank 1.

Welding of the strap 6 over its entire length is carried out only for reasons of a simpler production, the desired effect already being provided when the strap 6 is welded to the tank only at two anchor points 10, for example.

The strap 6 can also encompass the tank by its full extent, for example, as is shown in Figure 1.

A further variant of the tank 1 according to the invention is shown in Figure 6, wherein the tank 1 is encompassed by two straps 6 in a crossover arrangement. Another design of the tank 1 according to the invention is shown in Figures 7 and 8. This tank 1 is provided with a dome-shaped indentation 12, in the region of which the side walls 3 are welded to each other. This wall-to-wall weld, or this "kissing point", constitutes a structure which altogether stiffens the tank geometry, wherein the side wall 3 of the tank 1 (on the side facing the viewer in Figure 7) is reinforced by altogether four straps 6 which extend in each case between the indentation 12 and an edge 5 of the tank 1. The straps 6 are laid in each case in the region of their deflection around the edges 5 and around the periphery 13 of the indentation 16, wherein in this case a weld can again be provided over the entire length of the straps 6 or only in the region of the deflection of said straps 6. A further variant of the tank 1 according to the invention is shown finally in Figure 9. Inside the tank, provision is made for a support element 14 which extends between the end walls 4. The anchor points 10 on the outer skin of the tank 1 for the strap 6 are provided for example on the end faces 4 in the region of the inner-side abutment of the support element 14, wherein the strap 6 supports the bottom side walls 3 of the tank 1. The result of bulging of the tank 1 in this region would be that the tension upon the strap 6 would have the effect of the end walls 4 of the tank shifting towards each other, wherein this possible degree of freedom of the end walls 4 is resisted via the support element 14.

Instead of such a support element 14, structure- reinforcing measures, for example, may be provided in the end walls 4 in question of the tank, for example the end walls 4 may have a corresponding cross- sectional profile, or the end walls 4 may be of an inwardly curved design with a cylindrical or semi- cylindrical contour. The curvature may also extend only over sections of the end walls. For example, inwardly and/or outwardly projecting ribs may also be provided, extending over the height of the tank 1 into the side walls .

The tank wall which is shown in Figure 10 is provided for example as part of the tank bottom surface or as the entire tank bottom surface with a rib profile 15 which is spanned by two straps 6. The rib profile may have for example ribs and grooves extending parallel to each other, with a trapezoidal cross-sectional profile, for example, and forms a structural stiffening of the tank bottom surface, for example. The straps 6 are welded in each case to these ribs in the region of the outwardly projecting tops of said ribs. As a result of this, the area moment of inertia of the tank wall 2 in question is increased and sagging of the tank wall 2 in question is reduced by means of the straps which are loaded exclusively under tension. As a result of the spot welding of the straps 6 on the ribs, a force absorption is displaced into the adjoining tank walls 2.

List of designations

1 Tank

2 Tank walls

3 Side walls

4 End walls

5 Edges

6 Strap

7 Roll

8 Corners

9 Recess

10 Anchor points

11 Channel

12 Indentation

13 Periphery

14 Support element

15 Rib profile