FR2898549A1 - Manufacturing method for plastic fuel tank for automotive vehicle, involves welding peripheral and border regions of film into fuel tank wall and around accessory projected out from wall - Google Patents

Abstract

A film (22) with a peripheral region (28) and a border region (30) around the opening is placed on a fuel tank wall (10). The projection (24) of the accessory (14) e.g. vent valve, on the tank wall juts out of the film through the opening. The peripheral and border regions are welded on the tank wall and around the accessory, respectively, by laser or infrared radiation.

Description

A method of manufacturing a fuel tank and a tool for its implementation

  The present invention relates to a method of manufacturing a fuel tank of plastics material impermeable to gases and liquids. The invention also relates to a vacuum tool used to implement the method.

  Plastic fuel tanks used in industry, particularly in the automotive industry for equipping vehicles, generally comprise one or more accessories associated with them such as ventilation and venting valves. sampling pipettes, various sensors and their connections, the gauge and pump modules.

  These fuel tanks must meet ever more stringent sealing and permeability standards. The allowable emission limits have become so low that the leakage and permeability losses of the accessory interfaces with the reservoir have taken a higher relative proportion in the total losses of the reservoir + accessory system.

  It is known, from the patent application WO 01/21428, to seal multilayer plastic tank openings made to introduce or fix an accessory in the tank by means of a multilayer structure plate compatible with that of the tank, that we weld on the outer wall of the latter.

  In this document, however, it is disclosed that the plates used are of rigidity close to that of the walls of the tank. As a result, these plates can not be used easily when the emergent part of an accessory is too large, or the emergent surface of the accessory is irregular. In addition, despite the boss that can be made near the edge of the plate to locally reduce the thickness of the plastic layers constituting the multilayer plate, the level of fuel losses by emission at the weld site The plate on the tank still often remains too high and sometimes still exceeds the very low limits imposed by the new environmental standards.

  The patent application WO 03/035424 proposes a method of manufacturing a fuel tank in which a flexible film of multilayer structure, comprising at least one fuel barrier layer, is secured to the reservoir by a weld on the outer surface of the fuel tank. the latter, on the whole periphery of the film.

  Such a method makes it possible to manufacture a reservoir in which the emissions at the interfaces between the reservoir and the accessory are further reduced. Since the film is secured to the tank wall by welding over its entire periphery, good impermeability is obtained. The quality of impermeability, however, depends on the quality of the weld. The laser welding technique requires contact between the surface of the reservoir and the film to be welded. Indeed, the fuel tank generally has a non-planar and deformable surface. Therefore, the intimate contact between the latter and the film is difficult to obtain. When a gap exists between the surfaces, the heating of the flexible film by the laser radiation becomes non-homogeneous and difficult to control. Nonhomogeneous heating can lead to so-called cold zones and so-called burned zones. In cold areas, the weld is generally not resistant to the mechanical tests of the quality procedure in force. In burned areas, the flexible film is burned or, more accurately, the barrier layer of the film is altered and becomes permeable to hydrocarbons. It is therefore important, to obtain a good quality of welding, to improve the contact between the flexible film and the outer surface of the fuel tank. The object of the present invention is to provide a method of manufacturing a fuel tank with better impermeability to the interfaces between tank and accessory. Another object of the present invention is to provide a vacuum tool used to implement this method. The invention therefore relates to a method for manufacturing a plastic fuel tank, the tank being provided with at least one accessory connected to the interior of the tank via at least one orifice in the wall of this tank, this method comprising the steps of providing a flexible film and placing it on the reservoir so as to cover the interface between the reservoir and the accessory; and to weld the film over its entire peripheral zone on the tank wall. According to an important aspect of the invention, before welding, a vacuum is created between the flexible film and the wall of the tank. Thanks to such a depression, the interstices between the flexible film and the tank wall are minimized to thereby improve the contact between the surfaces.

  The intimate contact between these surfaces leads to a more homogeneous weld, that is to say to a weld in which cold areas and burnt areas are avoided. Thus, we obtain a better quality weld and increased impermeability at the interface between the reservoir and the accessory. According to the invention, by covering the interface between the reservoir and the component, is meant in fact to be arranged so as to cover both the periphery of the accessory and the wall of the reservoir surrounding it. In the context of the invention, by fuel tank is meant any type of tank capable of storing a liquid fuel and / or gas under varying pressure and temperature conditions. More particularly referred to are the tanks of the type found in motor vehicles. In the term "motor vehicle" is meant to include cars, motorcycles and trucks. By plastic material is meant any material comprising at least one synthetic resin polymer.

  All types of plastics may be suitable. Well-suited plastics belong to the thermoplastics category. Thermoplastic means any thermoplastic polymer, including thermoplastic elastomers, and mixtures thereof. The term "polymer" denotes both homopolymers and copolymers (especially binary or ternary). Examples of such copolymers are, but are not limited to: random copolymers, block copolymers, block copolymers and graft copolymers. Any type of thermoplastic polymer or copolymer whose melting point is below the decomposition temperature is suitable. Synthetic thermoplastics having a melting range spread over at least 10 degrees Celsius are particularly suitable. Examples of such materials are those having a polydispersion of their molecular weight.

  In particular, it is possible to use polyolefins, polyvinyl halides, thermoplastic polyesters, polyketones, polyamides and their copolymers. A mixture of polymers or copolymers may also be used, as well as a mixture of polymeric materials with inorganic, organic and / or natural fillers such as, for example, but not limited to: carbon, salts and other inorganic derivatives, natural or polymeric fibers. It is also possible to use multilayer structures consisting of stacked and solid layers comprising at least one of the polymers or copolymers described above. Polyolefins gave good results. Of the polyolefins, high density polyethylene (HDPE) is preferred.

  The invention is directed to a fuel tank provided with at least one accessory located at least partly outside the tank. By accessory is meant any organ in general through which liquid or gas passes, or which is in contact with liquid or gas and which performs a particular function of the fuel device which includes the tank, including a function of transporting liquid and / or gas between two other organs. Examples of such accessories include, but are not limited to, the following accessories: a container containing any chemical or physical composition, including a vapor absorption canister; a liquid or gas gauge; an electrical connection leading to a liquid or gas gauge; a liquid or gas pump; a safety valve ensuring the controlled closure of the tank in certain particular situations; a drainable capacity to collect liquid; an electrical power supply connection of the engine of a liquid or gas pump; a liquid pipe leading to a device for supplying any device, in particular to a motor; a liquid-vapor separation device. It is also possible to use any combination of at least two accessories, possibly in the presence of several copies of the same accessory. The accessory according to the invention may be of any material. However, preferably, it is mainly based on plastic and in particular, a plastic whose dimensional stability is not affected by the contact with the liquids and gases that may be contained in the reservoir, and which there is not very permeable. Polyacetals, polyamides, polyesters and polyvinyl halides give good results. Plastics that are well suited are polyacetals and in particular, POM (or poly-oxy-methylene). Most preferably, the accessory is at least partly made of injected plastic, i.e. having been shaped by a technique of injection molding under pressure in a mold.

  The accessory may be based on a material having low permeability to fuels, or polyethylene. Preferably, when the component is based on polyethylene, it is treated to reduce its permeability. The treatment consists, for example, in the sulfonation or the fluorination of the component.

  The accessory can be attached to the tank in any suitable manner. It can for example be attached by clipping (preferably with an intermediate seal to ensure sealing), or by welding. In the latter case, however, this implies that the part to be welded is compatible with the constituent material of the tank. In the case of a component mainly made of POM for a HDPE tank, one can for example make the bi-material component (for example by over-injection of HDPE on the POM). The accessory is located at least partly outside the tank. The accessory can be located completely outside the tank. An example is a module mounted on a wall of the tank and fulfilling a particular function involving the presence of fuel. The accessory may also be located only partially out of the tank. In this case, it passes through the wall thereof and is provided with an interface with this wall which provides a seal relative to gases and liquids. The accessory is covered with a protective device that improves the impermeability of the tank-accessory assembly. In other words, the presence of the protective device significantly reduces the fuel losses at the interface of the accessory with the tank. This protective device is a flexible film, preferably of multilayer structure, that is to say a laminated structure resulting from the stack of several layers each comprising at least one thermoplastic material and the thickness and nature of the layers such that the flexibility of the flexible film is substantially greater than that of the wall of the tank. Preferably, the flexible film is easily deformable by simple manual action. The flexible film has a surface of various natures. It may, for example, form a convex surface of shape delimited by more or less circular circular lines, elliptical or on the contrary with sharp angles such as rectangular or polygonal shapes. The flexible film may also have a non-convex surface comprising at least one convex surface located inside the surface of the flexible film. In each of these convex surfaces included in the non-convex surface of the flexible film, the multilayer structure is interrupted to leave room for a vacuum enclosed in the non-convex surface. According to the invention, the flexible film may be solid (continuous) or it may comprise an opening (generally central) for an element protruding from the accessory extending towards the outside of the reservoir, such as for example a pipe. This is particularly the case when the accessory is a valve connected to a ventilation line. The manner of using such films is the subject of a co-pending application or name of the plaintiff. These films are commonly called donut-shaped films. According to the invention, the flexible film advantageously comprises at least one fuel barrier layer. By fuel barrier layer is meant a layer impervious to gaseous and liquid fuels. The barrier layer generally comprises a barrier resin. Any known barrier resin may be present in the barrier layer, provided that it is effective with respect to fluid fuels likely to be in contact with the reservoir and / or the accessory, in particular hydrocarbons and that it is compatible with the technique of manufacturing the structure of the multilayer film. Among the possible resins include, but are not limited to, polyamides or copolyamides and random copolymers of ethylene and vinyl alcohol. A mixture of different barrier resins is also possible. Very good results have been obtained with a barrier layer comprising a barrier resin random copolymer of ethylene and vinyl alcohol. The flexible film may have been obtained by any known technique leading to the manufacture of a thin and flexible multilayer structure. One possible technique is the technique of extruding a multilayer film through a flat die. Another possible technique is the compression molding of a multilayer plate. The flexible film covering the tank accessory is, according to the invention, secured to the reservoir (in the vicinity: around the component) by a weld. The flexible film may, for example form a pocket trapping an accessory, which is welded to the reservoir. The welding of the flexible film is located on the outer surface of the reservoir, over the entire outer peripheral zone of the film. In the case where the film is of the donut type as mentioned above, the film is preferably also welded to the entire border zone around the opening in the film, on the surface of the accessory. Such a method makes it possible to secure the film by welding, not only in its peripheral zone, but also in its border zone around the opening. In this variant, surprisingly, the Applicant has found that it was sufficient to evacuate (to create a depression) at the periphery of the film, and that it was not necessary to do it around the periphery of the film. opening, and this by the staircase geometry of the film (which spans the accessory), which reduces the path of escape. This path can be further reduced by modifying the geometry of the film so that the aperture is in a hollow (or concave relief) of the film (ie, making the last step of the film staircase - the one that leads to the opening - is slightly downward, so as to naturally ensure the seal by pressing the accessory). The welding of the flexible film can be of varied nature. All types of welding compatible with the plastics to be assembled are suitable. Preferably, the nature of the weld is of the infrared or laser radiation welding type, the latter being very particularly preferred. In this case, the flexible film may advantageously be welded to a wider peripheral zone than with other types of welding. Such a wide area can be obtained by successive and parallel scans, overlapping partially.

  Thus, it is possible in practice to make 1 to 6 passes of 4 to 5 mm wide so as to achieve a weld whose width can vary from 4 to 18 mm. According to a preferred embodiment, the vacuum is made under the use of a vacuum tool on the periphery of the flexible film, this vacuum tool (which will be described in detail below) comprising a suction chamber placed on any the periphery of the flexible film and at least one suction channel for evacuating the air from the suction chamber. Thus, the suction chamber 8 is able to suck the air under the flexible film so as to create an intimate contact between the flexible film and the wall of the tank, respectively the accessory. The air is evacuated from the suction chamber by the at least one suction channel connected to a suction pump.

  Preferably, the depression is made by applying relative depression in the range of -800 to -60 mbar. Such a depression ensures an intimate contact between the flexible film and the support on which it rests. Advantageously, pressure is exerted on the weld region after and / or before the weld, especially when it occurs by laser radiation. Pressurizing the weld region, after and / or before the weld (but in particular after), locally increases the pressure of the flexible film on the reservoir to thereby improve the intimate contact between the flexible film and the wall of the fuel tank. The pressure can be exerted by means of a pressure device, such as a rotary roller or a pad. In the case of a thick film, a pad is generally preferred, the sliding principle replaces the rotating system of a roller, too fragile under high pressure. By pad is meant a kind of shoe provided with an opening by which the laser beam can operate the welding (by a principle similar to that of a sewing machine). This tool has the advantage of applying a continuous and uniform pressure all around the weld zone during the production thereof. When using a rotary roller against, it can apply pressure in one place (just before or just after welding / laser beam). The local increase in the pressure of the flexible film on the tank ensures a better melting of the materials, particularly in the case of a fuel tank with an irregular surface. It also ensures a better conformation of the flexible film to the geometry of the reservoir and / or the accessory, in particular in the case of a fuel tank with concave and / or convex shapes on at least a part of the welding path . Preferably, the pressure exerted is in the range of 6 to 18 bar. The present invention also relates to a vacuum tool used to implement the method described above. According to the invention, such a vacuum tool (for creating a vacuum between a support and a flexible film placed on the support) comprises a suction chamber comprising an opening directed both to the flexible film and to the support the opening of the suction chamber being -9 peripheral (ie capable of overlapping / stepping over the edge of the flexible film over its entire periphery); and at least one suction channel for sucking air from the suction chamber. Preferably, the tool comprises several suction channels (at least 3, or even 6 or even 8), preferably distributed homogeneously around the periphery of the film. According to a preferred embodiment, the vacuum tool comprises, at the opening of the suction chamber, a peripheral seal whose first portion is intended to bear on the flexible film and a second portion is intended to bear on the support, the suction chamber being disposed between the first portion and the second portion. When the vacuum tool is in its working position, that is to say placed on the flexible film, the first portion of the peripheral seal rests on the flexible film while the second portion of the peripheral seal rests on the support. The edge of the flexible film is thus positioned between the first and the second portion and is therefore in communication with the suction chamber disposed between the two portions. The start of a suction pump connected to the suction channel causes the suction of air from the suction chamber and, in turn, the space between the flexible film and the support. Thus, the air is evacuated beneath the flexible film. The depression thus formed causes the flexible film to come into intimate contact with the surface of the support. Advantageously, the peripheral seal is a lip seal and is arranged to form an enlarged suction chamber near the opening of the suction chamber. By this means a directly molded U-shaped inverted seal, or a relatively wide circular seal in which one machines a groove whose width is greater than that of the suction channel (see Figure 1). Thanks to the enlarged chamber, the positioning accuracy of the vacuum tool is less critical. In addition, better suction of the air below the flexible film is obtained. Alternatively (to a single machined lip seal), the peripheral seal could actually consist of two concentric circular seals. The peripheral seal is preferably a seal of deformable material, for example an elastomer, preferably expanded such as a cellular rubber. Indeed, given the additional thickness of the film in the inner area (accessory side), making the seal deformable avoids machining of one of the legs of the U as in Figure 1 attached to the - 10 - present memory (the accessory side leg is then more compressed than the tank side leg). Preferably, at least one pressure device arranged to exert a pressure on the film, in the weld zone, after and / or before welding (in particular when this occurs by laser radiation). This pressure device may for example be a rotary roller or a pad (see above). The pressure device makes it possible to exert pressure on the area of the film to be welded, thereby further improving the intimate contact between the flexible film and the support.

  The pressure device preferably comprises a pressure regulator. With such a pressure regulator, the pressure exerted by the pressure device on the flexible film can be controlled. Preferably the pressure is kept constant over the entire periphery of the flexible film. This pressure is preferably between 6 and 18 bar.

  Other features and characteristics of the invention will emerge from the description of an advantageous embodiment presented below, by way of illustration, with reference to the appended drawings, which show: FIG. cutting a portion of a vacuum tool according to one embodiment of the invention; and FIG. 2: a perspective view of a vacuum tool according to one embodiment of the invention. FIG. 1 shows a radial end of a vacuum tool 10 used to improve the contact between a flexible film 12 and a wall of a fuel tank 14. The vacuum tool 10 comprises a suction chamber 16 comprising a opening 18 facing both the flexible film 12 and the reservoir 14. The opening 18 of the suction chamber 16 is peripheral and formed so as to straddle the edge 20 of the flexible film 12 over its entire periphery. The vacuum tool 10 further comprises at least one suction channel 22 for discharging air from the suction chamber 16 (Figure 1 illustrating a cut through such a channel). The opening 18 of the suction chamber 16 is provided with a peripheral seal 24 directed both to the flexible film and to the reservoir 14. When the vacuum tool 10 is in its working position, as shown in fig. 1, a first portion 26 of the peripheral seal 24 rests on the flexible film 12 while a second portion 28 of the peripheral seal 24 rests on the reservoir 14. The edge 20 of the flexible film 12 is thus positioned between the first and the second second portion 26, 28 of the peripheral seal 24. Thus, the edge 20 of the flexible film 12 is in communication with the suction chamber 16 disposed between the two portions 26, 28. The startup of a suction pump ( not shown) connected to the suction channel 22 draws air from the suction chamber 16 and, in turn, from the space between the flexible film 12 and the reservoir 14. Thus, the air is evacuated below the flexible film 12. The depression thus formed ensures that the flexible film 12 comes into intimate contact with the wall of the reservoir 14. The flexible film 12 is preferably a multilayer film of circular shape with three layers, of 0 , 3 mm to 0.6 mm total thickness including a e EVOH barrier layer sandwiched between two HDPE layers, the HDPE layer facing the reservoir 14 being charged with 0.25% by weight of carbon black having been welded by means of a scanning of diode used in pulsed mode (FAP type laser, YAG wavelength of 809 nm and 35 W power). FIG. 2 shows a vacuum tool 30 comprising a support ring 32 to which is connected, by means of several bars 34, a vacuum ring 36. The vacuum tool 30 may further comprise a central gripping element 38 capable of take the flexible film and deposit it on both the tank and the component. For this purpose, the gripping member 38 may comprise a plurality of suction cups 40 connected to a vacuum means, eg a vacuum pump (not shown). According to another embodiment, it is possible to design a vacuum tool with a vacuum ring 36 also ensuring the role of support / installation of the film in the device. Thus, it is not necessary to provide the support ring 32 and the bars 34 of the illustrated embodiment. The vacuum ring 36 comprises a peripheral seal 24 comprising a first inner portion 26 and a second outer portion 28. The first and second portions 26, 28 are spaced radially so as to form a suction chamber 16. The first and second portions 26, 28 may be formed by two separate seal members with the suction chamber 16 disposed between the two on a lower part and a vacuum pump arranged between the two on an upper part. Alternatively, the first and second portions 26, 28 may be part of an inverted "U" shaped unitary joint element comprising two branches and a base. The suction chamber 16 is formed between the two branches of the seal member and a plurality of openings are machined in the base to connect the suction chamber 16 to the vacuum pump. The peripheral seal 24 is designed so that the suction chamber 16 has an inside diameter smaller than the diameter of the flexible film and an outside diameter larger than the diameter of the flexible film. Thus, the peripheral edge of the flexible film is, when the vacuum tool is in its working position, disposed between the two portions 26,28 and is in communication with the suction chamber 16. Preferably, the edge 20 the flexible film peripheral is disposed in the middle of the suction chamber 16, that is to say at equal distance of the two portions 26,28. The first portion 26 may have a length slightly shorter than the second portion 28. This difference preferably corresponds to the thickness of the flexible film, thus increasing the efficiency of the vacuum. Alternatively (and preferably), the U is symmetrical (as already mentioned above), hence a greater pressure / better support on the edge of the film. Key figures: 10 vacuum tool 12 flexible film 14 wall of a fuel tank 16 suction chamber 18 opening 20 edge 22 suction channel 24 peripheral seal 26 first portion of the peripheral seal 28 second portion of the peripheral seal tool depression 32 support ring 30 34 bar 36 vacuum ring 38 gripping element 40 suction cup

Claims (10)

  A method for manufacturing a plastic fuel tank having at least one accessory connected to the interior of the tank via at least one port in the wall (14) of the tank, said method comprising the steps of: providing a flexible film (12) and placing it on the reservoir so as to cover the interface between the reservoir and the accessory; and - soldering the film (12) over its entire peripheral zone on the wall (14) of the reservoir; characterized in that, prior to welding the film (12) on the wall (14) of the tank, a vacuum is created between the flexible film (12) and the wall (14) of the tank.   2. Method according to the preceding claim, characterized in that the vacuum is in a range of -800 to -60 mbar.   3. Method according to any one of the preceding claims, characterized in that the welding takes place by laser radiation and in that, after and / or before welding, a pressure is exerted on the weld region.   4. Method according to the preceding claim, characterized in that the pressure exerted is in a range from 6 to 18 bar.   5. Method according to any one of the preceding claims, characterized in that the flexible film (12) is of multilayer structure comprising at least one barrier layer fuels.   Depression tool (10, 30) for creating a depression between a support (14) and a flexible film (12) placed on the support and suitable for a method according to any one of the preceding claims, characterized in that it comprises: a suction chamber (16) comprising an opening (18) directed both to the flexible film (12) and to the support (14), the opening (18) of the suction chamber being peripheral and formed so as to span the edge of the flexible film (12) over its entire periphery; and at least one suction channel (22) for sucking air from the suction chamber (16).   7. Tool according to the preceding claim, characterized in that it comprises, at the opening (18) of the suction chamber (16), a peripheral seal (24), a first portion (26) is intended to take pressing on the flexible film (12) and a second portion (28) is intended to bear on the support (14), the suction chamber (16) being arranged between the first portion (26) and the second portion (28). ).   8. Tool according to the preceding claim, characterized in that the peripheral seal (24) is a lip seal and is arranged to form an enlarged suction chamber near the opening of the suction chamber (16) .   9. Tool according to any one of claims 6 to 8, characterized by at least one pressure device arranged to exert pressure on the film in the weld zone, before and / or after welding.   10. Tool according to the preceding claim, characterized in that the pressure device comprises a pressure regulator.