WO2007122185A1

WO2007122185A1 - Method of manufacturing a fuel tank

Info

Publication number: WO2007122185A1
Application number: PCT/EP2007/053867
Authority: WO
Inventors: Philippe Martin; Stéphane Leonard; Richard Lesschaeve; Pierre-François TARDY; Barbara Mabed
Original assignee: Inergy Automotive Systems Research (Société Anonyme)
Priority date: 2006-04-21
Filing date: 2007-04-20
Publication date: 2007-11-01
Also published as: FR2900092A1

Abstract

Method for manufacturing a plastic fuel tank provided with at least one accessory connected to the internal space of the tank via at least one orifice (12) in the wall (10) of the tank. The method comprises the steps consisting in: providing a multilayer film (16), that includes at least one fuel-barrier layer; providing a cover (14) intended to cover the orifice (12) in the wall (10) of the tank; fastening the cover (14) to the multilayer film (16), thus forming a fuel-barrier cover/film assembly (13); covering the orifice (12) in the wall (10) of the tank with the cover/film assembly (13); and attaching the cover/film assembly (13) to the fuel tank.

Description

Method of manufacturing a fuel tank

The present invention relates to a method of manufacturing a plastic fuel tank impermeable to gases and liquids.

Plastic fuel tanks used in industry, in particular in the automotive industry for equipping vehicles, generally include one or more accessories that are associated therewith, such as aeration and venting valves, filling pipes, various sensors and their connections, gauge and pumping modules. Such accessories are generally mounted in an orifice provided in the wall of the fuel tank.

These fuel tanks must meet increasingly stringent sealing and permeability standards. The permitted emission limits have become so low that losses associated with leakage and with permeability at the tank/accessory interfaces have taken a relatively higher proportion in the total losses from the tank/accessory system.

Thus, in particular the latest standards in force in the United States impose, for fuel systems with which motor vehicles are equipped, increasingly smaller evaporative loss values. As an example, the losses permitted for the entire vehicle during a standardized daily cycle (CARB) have gone from 2 g/day (LEVl requirement valid since 1996) to 0.5 g/day in 2004 (LEVII requirement). In addition, part of the motor vehicle fleet must since 2003 meet the PZEV (Partial Zero Emission Vehicle) standards which limit the losses of just the fuel system to 54 mg/day.

It is known, from Patent Application WO 01/21428, to close off openings in the multilayer plastic tank, which are provided for introducing or fastening an accessory in the tank, by means of a plate of multilayer structure compatible with the structure of the tank, which is welded to the external wall of the latter. This multilayer plate is advantageously obtained from tank production scrap by pressing (compression moulding) two identical pieces cut from them. This constitutes an additional manufacturing step.

In that document, it is also stipulated that the plates used should have a stiffness similar to that of the walls of the tank. As a result, these plates cannot be easily used where the emergent part of an accessory is too bulky, or when the emergent surface of the accessory is irregular. In addition, despite the bulge that can be produced near the edge of the plate, so as to locally reduce the thickness of the plastic layers constituting the multilayer plate, the level of fuel losses by emission at the weld between the plate and the tank often still remains too high and sometimes even exceeds the very low limits imposed by the latest environmental standards, such as for example the PZEV standards.

Patent Application WO 03/035424 provides a method of manufacturing a fuel tank in which a flexible film of multilayer structure, which includes at least one fuel-barrier layer, is placed on top of the multilayer plate and fastened to the tank by welding it to the outer wall of the latter over the entire periphery of the film. Such a method allows a tank to be manufactured in which the emissions at the interfaces between the tank and the accessory are further reduced. If the accessory is completely covered by the film, very good impermeability compatible with the PZEV standards is obtained. Manufacturing fuel tanks using such a method requires two fastening operations: a first one for fastening the plate and a second for fastening the film. In certain cases, such a method may be considered to be too long and too expensive. Furthermore, there is a risk of the multilayer film swelling as a result of fuel vapour passing over the course of time through the plate. Such swelling may result in the formation of a large bubble which, upon possible contact with the chassis of the vehicle and/or the accessories present near the tank, may result in the film becoming damaged, for example by rubbing. This therefore leads to a reduction in the impermeability conferred by the system.

The object of the present invention is therefore to provide a more rapid and less expensive method of manufacturing a fuel tank with very good impermeability, even in the long term.

According to the invention, this objective is achieved by a method for manufacturing a plastic fuel tank provided with at least one accessory connected to the internal space of the tank via at least one orifice in the wall of the tank. According to the invention, the method comprises the steps consisting in providing a multilayer film, that includes at least one fuel-barrier layer; providing a cover intended to cover the orifice in the wall of the tank; fastening the cover to the multilayer film, thus forming a cover/film assembly; covering the orifice in the wall of the tank with the cover/film assembly; and attaching the cover/film assembly to the fuel tank. The manufacture of the fuel tank is made simpler and more rapid by the fact that the cover attached to the fuel tank has already been provided with the fuel-barrier multilayer film. The steps of handling and accurately positioning the multilayer film on the cover are consequently no longer necessary. This simpler and more rapid method also entails a reduction in the manufacturing cost of the fuel tank.

Another advantage of the method according to the invention is the better bonding between the cover and the multilayer film. This is because, thanks to the bonding between the cover and the multilayer film, the abovementioned swelling of the film, and the risks associated therewith, may be avoided.

Another advantage is that the method according to the invention may be suitable at the same time for providing a solution that meets the LEVII or PZEV requirements. This point will be discussed in detail later.

The term "fuel tank" is understood to mean any type of tank capable of storing a liquid and/or gaseous fuel under varied pressure and temperature conditions. More particularly intended are tanks of the type of those encountered in motor vehicles. The term "motor vehicle" is intended to include motor cycles and lorries just as well as cars.

The term "plastic" is understood to mean any material comprising at least one synthetic resin polymer.

All types of plastics may be suitable. Particularly suitable are plastics that belong to the category of thermoplastics.

The term "thermoplastic" is understood to mean any thermoplastic polymer, including thermoplastic elastomers, and blends thereof. The term "polymer" is understood to mean both homopolymers and copolymers

(especially binary or ternary copolymers). Examples of such copolymers are, non-limitingly, random copolymers, linear block copolymers and other block copolymers, and graft copolymers.

Any type of thermoplastic polymer or copolymer, the melting point of which 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 include those that exhibit polydispersion in their molecular weight.

In particular, polyolefins, polyvinyl halides thermoplastic polyesters, polyketones, polyamides and their copolymers may be used. A blend of polymers or copolymers may also be used, as well as a blend of polymeric materials with inorganic, organic and/or natural fillers such as, for example, but not limitingly: carbon, mineral fillers, clay, montmorillonite, salts and other inorganic derivatives, and natural or polymeric fibres. It is also possible to use multilayer structures consisting of stacked layers bonded together, comprising at least one of the polymers or copolymers described above.

Polyolefins have given good results. Among polyolefins, high-density polyethylene (HDPE) is preferred.

The invention relates to a fuel tank provided with at least one accessory located at least partly on the outside of the tank. The term "accessory" is understood to mean any member in general via which liquid or gas can pass, or which is in contact with liquid or gas and which fulfils a particular function specific to the fuel system of which the tank forms part, including the function of transporting liquid and/or gas between two other members.

Examples of such accessories comprise, but not limitingly, the following accessories:

• a container for containing any chemical or physical composition, especially a vapour absorption canister;

• a liquid or gas gauge;

• an electrical connection terminating in a liquid or gas gauge; a liquid or gas pump;

• a safety valve, ensuring controlled closure of the tank in certain particular situations;

• a drainable tank, for collecting liquid;

• an electrical connection for powering the motor of a liquid or gas pump; • a liquid line terminating in a system for supplying any device, especially an engine;

• a liquid/vapour separator; and

• a connection to a filling pipe.

It is also possible to use any combination of at least two accessories, possibly in the presence of several examples of the same accessory.

The accessory may be completely on the outside of the tank. One 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 partly on the outside of the tank. In this case, it passes through the wall of the tank and is provided with an interface with this wall that ensures relative impermeability 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 between the accessory and the tank. This protective device is a fuel-barrier/cover film assembly, which will be described in greater detail below.

The film has a multilayer structure, that is to say a laminated structure preferably resulting from the stacking of several layers each comprising a thermoplastic. According to the invention, the multilayer film includes at least one fuel-barrier layer. The term "fuel-barrier layer" is understood to mean a layer impermeable 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 against fluid fuels liable to be in contact with the tank and/or the accessory, particularly hydrocarbons, and provided that it is compatible with the technique of producing the structure of the multilayer film. Among possible resins, mention may be made, non-limitingly, of polyamides or copolyamides and random ethylene/vinyl alcohol copolymers (EVOH). The fuel-barrier layer is preferably a barrier layer based on an ethylene/vinyl alcohol copolymer (EVOH) and/or, to a lesser extent, a polyamide (PA). A blend of various barrier resins is also possible. Very good results have been obtained with a barrier layer comprising a barrier resin made of a random ethylene/vinyl alcohol copolymer.

The multilayer film may have been obtained by any known technique resulting in the production of a thin flexible multilayer structure. One possible technique is that of extruding a multilayer film through a sheet die. Another possible technique is the compression moulding of a multilayer plate. As regards the cover, this is preferably also based on a plastic. The term "cover" is in general intended to mean an object having the form of a plate, i.e. a flat and quite thin element made of rigid material. For comparison, the film is thinner than the cover and has a certain flexibility. The cover may have a structure made of a monolayer or multilayer plastic.

Preferably, a single -material cover made of high-density polyethylene (HDPE) is used within the context of the invention. This cover is preferably manufactured from the same plastic as the fuel tank, or at least the cover and the tank have their outer layer based on the same material or on a compatible material so as to be able to be assembled by welding (see later). Likewise, the cover and the film preferably have at least one external layer compatible with or based on the same material. Thus, in a preferred embodiment, the cover is made of HDPE and the multilayer film comprises a barrier layer, preferably made of EVOH, and at least one external layer also made of HDPE. According to the invention, the cover and the multilayer film are objects manufactured separately and assembled as required before being fastened over the top of the orifice in the tank. This fastening operation may be carried out in any known manner.

The fastening of the cover to the multilayer film may for example be carried out by moulding the cover over the multilayer film, by welding the multilayer film to the cover or by bonding the multilayer film to the cover.

Preferably, the step consisting in fastening the cover to the multilayer film is followed by storage of a fuel-barrier/cover film assembly thus manufactured. Fuel-impermeable cover/film assemblies may thus be prefabricated and used when manufacturing a fuel tank, whatever the impermeability standard to be met. Using prefabricated assemblies further speeds up the method of manufacturing fuel tanks since all that is required is to handle a single component for covering the orifice in the wall of the fuel tank. The fuel- impermeable cover/film assemblies may also be prefabricated at any place and transported to the place where the fuel tank is manufactured. Thus, it is possible to produce fuel- impermeable cover/film assemblies in bulk, so as in this way to reduce the manufacturing costs.

According to one embodiment, the cover/film assembly is an assembly that completely closes an orifice in the wall of the tank. According to another embodiment, the cover/film assembly includes a fluid passage, the cover having a first opening and the multilayer film having a second opening, the second opening being aligned with the first opening. Such a cover/film assembly allows a line to be placed through the cover/film assembly, the line allowing communication between the inside and the outside of the tank. Advantageously, the multilayer film includes at least one layer containing a polyolefin.

The cover may be moulded over the multilayer film by injection moulding. Among injection moulding processes, mention may be made of overmoulding or "in-mould decoration". Thus, the cover is fastened to the multilayer film during its formation. The film may also be welded or bonded to the cover after it has been formed, but this is a less advantageous variant as it involves an additional manufacturing step.

Hot-plate welding may be used to weld the cover to the fuel tank. Ultrasonic welding or vibration welding is also possible. After the cover has been fastened to the fuel tank, the film may also be welded to the tank by hotplate, ultrasonic, infrared or even laser welding.

According to one embodiment, the cover and the multilayer film are in contact over their entire area. The cover and the multilayer film therefore have exactly the same dimensions. Such a fuel-barrier cover may be used to meet the permeability standard at the LEVII level.

According to another embodiment, the cover and the multilayer film are in contact only over part of the area of the multilayer film, the latter extending beyond the cover over its entire periphery. In this embodiment, the diameter of the multilayer film is therefore greater than the diameter of the cover. The multilayer film may for example extend beyond the diameter of the cover by 10 to 80 mm over its entire periphery. Such a fuel-barrier cover/film assembly meets the permeability standard at the PZEV level since the film in fact covers the entire weld zone between the cover and the tank. The dimensions of the extension part of the multilayer film may for example depend on the shape of the tank or on the desired impermeability.

That part of the multilayer film extending beyond the cover may be welded to the external surface of the fuel tank, preferably after the cover has been welded to the tank. All types of welding compatible with the plastics to be assembled are suitable for this purpose. Preferably, the welding is laser welding, infrared welding or ultrasonic welding. The welding of the multilayer film is preferably localized over the entire outer peripheral region of the multilayer film. Compared with the solution of application WO 01/21428 described above, the present invention has a certain economic advantage. This is because it is more advantageous to use a cover that is injection-moulded over (or welded to) the multilayer film produced beforehand (or even commercially available). This is because the abovementioned production of multilayer plates is no longer necessary and the system according to the invention may be used to meet both standards at the same time. The sole difference results from the diameter of the film used. If the film has the same diameter as the cover, it provides an LEVII solution, whereas if the film is wider than the cover, its circumference may be welded to the tank and a PZEV solution may be obtained. In fact, whatever the standard intended, the initial step is identical and consists in injection-moulding or welding an HDPE cover to a larger-diameter multilayer film. Next, in the case of LEVII solutions, a step of cutting the film to the diameter of the cover is necessary, whereas for PZEV solutions a step of welding (preferably laser welding) the film extending beyond the cover to the tank is necessary.

Other particular aspects and features of the invention will become apparent from the description of a few advantageous embodiments presented below, by way of illustration, with reference to the appended drawings. These show:

Figure 1 , a sectional schematic view of a fuel-barrier cover/film assembly mounted on an orifice of a fuel tank manufactured according to one embodiment of the invention; and

Figure 2, a sectional schematic view of a fuel-barrier cover/film assembly mounted on an orifice of a fuel tank manufactured according to another embodiment of the invention. In the figures, the same reference numbers denote identical elements.

Figures 1 and 2 show a wall 10 of a fuel tank in which an orifice 12 for mounting an accessory (not shown) is provided. To close off the orifice 12 after the accessory has been mounted, a cover/film assembly 13 is mounted on the wall of the fuel tank so as to cover the orifice 12. Such a cover/film assembly 13 is formed by fastening a cover 14 to a multilayer film 16 that includes at least one fuel-barrier layer. The cover 14 may be moulded over or welded to the multilayer film 16.

The multilayer film 16 may for example comprise five layers, with a total thickness of 0.6 mm, including an EVOH barrier layer between two adhesive layers, these all being sandwiched between two HDPE layers, the HDPE layer placed on the wall 10 of the tank typically being filled with 0.25% by weight of carbon black.

In the embodiment shown in Figure 1, the cover 14 and the multilayer film 16 have the same dimensions. Such a cover/film assembly 13 is designed to meet the permeability standard to the LEVII level.

In the embodiment shown in Figure 2, the multilayer film 16 is larger than the cover 14. In fact, the multilayer film 16 has, over the entire periphery of the cover 14, an extension region 18, extending for example by 10 to 80 mm. This extension region 18 allows the film to come into direct contact with the wall 10 of the fuel tank. The extension region 18 may therefore be welded to the wall 10 for example by scanning with diode laser radiation used in pulsed mode (FAP, YAG type laser). The extension region 18 is preferably welded over its entire periphery. Such a cover/film assembly 13 is designed to meet the permeability standard to the PZEV level.

Claims

C L A I M S

1. Method for manufacturing a plastic fuel tank provided with at least one accessory connected to the internal space of the tank via at least one orifice (12) in the wall (10) of the tank, the method comprising the steps consisting in:

• providing a multilayer film (16), that includes at least one fuel-barrier layer;

• providing a cover (14) intended to cover the orifice (12) in the wall (10) of the tank;

• fastening the cover (14) to the multilayer film (16), thus forming a cover/film assembly (13);

• covering the orifice (12) in the wall (10) of the tank with the cover/film assembly (13); and

• attaching the cover/film assembly (13) to the fuel tank.

2. Method according to the preceding claim, in which the cover (14) is fastened to the multilayer film (16) by moulding the cover (14) over the multilayer film (16), by welding the multilayer film (16) to the cover (14) or by bonding the multilayer film (16) to the cover (14).

3. Method according to one of the preceding claims, in which the step consisting in fastening the cover (14) to the multilayer film (16) is followed by storage of the fuel-barrier cover/film assembly (13) thus manufactured.

4. Method according to any one of the preceding claims, in which the cover (14) is a single-material cover made of high-density polyethylene (HDPE).

5. Method according to any one of the preceding claims, in which the cover/film assembly (13) includes a fluid passage, the cover (14) having a first opening and the multilayer film (16) having a second opening, the second opening being aligned with the first opening.

6. Method according to any one of the preceding claims, in which the multilayer film (16) is a film that includes at least one layer containing a polyolefin.

7. Method according to any one of the preceding claims, in which the fuel-barrier layer is a barrier layer based on an ethylene/vinyl alcohol copolymer (EVOH) and/or a polyamide (PA).

8. Method according to any one of the preceding claims, in which the step consisting in attaching the cover/film assembly (13) to the fuel tank is carried out by hot-plate welding, ultrasonic welding or vibration welding.

9. Method according to any one of the preceding claims, in which the cover (14) and the multilayer film (16) are in contact over their entire area.

10. Method according to any one of Claims 1 to 8, in which the cover (14) and the multilayer film (16) are in contact only over a part of the area of the multilayer film (16), the latter having an extension part (18) that extends beyond the cover (14) over its entire periphery.

11. Method according to the preceding claim, in which that part of the multilayer film (16) extending beyond the cover (14) is welded to the external surface of the fuel tank by laser welding, infrared welding or ultrasonic welding.