WO2000043230A1

WO2000043230A1 - Plastic fuel tank with pipe nipple

Info

Publication number: WO2000043230A1
Application number: PCT/CA2000/000011
Authority: WO
Inventors: Changize Sadr
Original assignee: Salflex Polymers Ltd.
Priority date: 1999-01-19
Filing date: 2000-01-04
Publication date: 2000-07-27

Abstract

A fuel tank system for use in automotive and similar applications helps to control vapour leakage which occurs where pipe or conduit nipples are attached to a multi-layer plastic fuel tank. The outer layer of the fuel tank is made from a modified polyolefin with anhydride or acrylate functionality. The hose fitting is selected from a material having a creep strain superior to that of the material of the outer layer and a tensile modulus of elasticity higher than that of the material of the outer layer. This gives a hose fitting to which a flexible conduit may be clamped in a seal which does not deteriorate because of creep failure while still permitting welding of the pipe fitting to the tank relatively readily.

Description

Title: PLASTIC FUEL TANK WITH PIPE NIPPLE

FIELD OF THE INVENTION

This invention relates to the field of hose connectors for attaching a conduit to a formed thermoplastic fuel tank. More particularly, the invention relates to liquid hydrocarbon containing fuel tanks such as those used in automotive applications.

BACKGROUND OF THE INVENTION

In the past fuel tanks for automobiles were manufactured from metals. Metals are good in preventing passage of hydrocarbon vapours through the walls of the tanks. More and more, it is becoming common to manufacture tanks, in particular gasoline tanks, for cars and trucks from thermoplastic formable resins. Often such tanks are made in blow molding procedures. As environmental concerns are addressed, it is becoming more and more important to ensure that hydrocarbon vapours do not pass through the walls of any of the components of the fuel system extending from the tank through to the internal combustion engine. In order to control and substantially inhibit the passage of hydrocarbon vapours through the walls of the fuel storage tank, it is now becoming more common to produce multi-layer fuel tanks. By using a plurality of layers and wherein one of those layers is a barrier material, the passage of fuel vapours through the tank wall can be substantially completely inhibited.

Routinely there are a host of connections to a fuel tank. Often the connections are in the form of hoses or conduits which typically are flexible. Such conduits are often intended to carry fuel vapours, either to or from the tank as part of a tank breathing system, a fuel vapour recirculation system and the like.

It has recently been recognized that with the substantial inhibition of fuel vapour passage through the walls of the tank, one of the remaining significant sources for fuel vapour leakage relates to the connection of such conduit to the fuel tank. One of the most common ways of affixing pipe nipples to a thermoplastic fuel tank is thermal welding. Welding of respective thermoplastic compounds is successful when the compounds are compatible with each other. Unsatisfactory welds, however, are often produced when compounds are not complimentary.

Typically, fuel tanks are manufactured from high density polyethylene. Even where multi-layer wall structures are used, the outer layer of the tank is typically high density polyethylene. This is a material which is well suited for the job in that it is relatively inexpensive, easily handled in forming operations such as blow molding and has the requisite strength and ruggedness to maintain the integrity of a fuel tank in automotive applications. Thus the material of choice for ease of welding for a pipe fitting would also be high density polyethylene. High density polyethylene, however, has been recognized to have one major disadvantage. The material is subject to creep when subjected to continuous stress such as compressive loading. In order to provide the desirably tight and hopefully vapour proof seal between the hose or conduit and the pipe fitting, hose clamps or the like may be used. In certain cases deformable rubberized o-rings may be also used to achieve the desired seal. However, in all cases, clamping pressure, whether with or without an o-ring works on the basis that the underlying structure will remain integral, that is, that its shape and dimension will not change over time and thus a clamp once tightened will remain tight. A significant problem with high density polyethylene is that under the continuous pressure of a hose clamp or the like, the underlying structure will creep. As creep occurs to release the stress involved, the clamp no longer fits as tightly as originally installed and even flexible materials such as rubber o- rings and the like will not provide as good a seal over passage of time as at the outset. This then gives rise to a possible vapour leakage at the joints between the conduit and the pipe nipple.

One solution for this problem is set out in U.S. patent number 5,443,098, Kertesa, issued August 22, 1995. According to Kertesa a solution to the problem involves manufacturing a two component pipe nipple. One component is manufactured from a material which is substantially resistant to creep. This portion of the pipe nipple can then be fitted with a hose and a suitable clamp to achieve the desired long lived seal. In order to make the pipe nipple of Kertesa, the material which is not subject to creep is inject molded about a second portion of the pipe nipple. The second portion of the pipe nipple is manufactured from material such as high density polyethylene. The joint between the two portions of the pipe nipple is closed by over molding during the injection molding process of the creep resistant material. By manufacturing the second portion of the pipe nipple from high density polyethylene, it is taught that the pipe nipple can be successfully welded to a tank having a high density polyethylene outer layer by rotational welding. This solution to the problem requires a more complicated pipe nipple manufactured from two different materials and requires an over molding during the injection molding aspect of the creep resistant portion.

SUMMARY OF THE INVENTION

In accordance with the present invention the fuel tank system comprises a fuel tank and a hose fitting. The fuel tank has a wall which comprises a plurality of layers of thermoplastic materials. The plurality of layers of the tank includes at least one barrier layer for inhibiting passage of hydrocarbon vapour through the wall of the tank. The plurality of layers further includes an outer layer. The hose fitting is made from material with mechanical properties suitable for its application. The material has a creep strain less than and a tensile modulus of elasticity higher than that of the material of the outer layer. The outer layer of the fuel tank is made from material which is mutually compatible with the material of the hose fitting for thermally welding the hose fitting to the fuel tank and is selected from the group consisting of modified polyolefin with anhydride and modified polyolefin with acrylate functionality.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be more clearly understood from reference to the attached drawing which illustrates by way of example a preferred embodiment of the invention, and in which:

Figure 1 illustrates, in partial cross-section, a portion of a fuel tank wall and a hose fitting welded thereto.

The fuel system 10 is illustrated generally in partial cross- section in Figure 1. The fuel system 10 comprises a fuel tank 12 and a fitting 14.

The fuel tank 12 comprises a wall 20. The wall 20 defines an aperture therethrough 22, through which fuel vapours may pass. Fuel vapours passing through the aperture 22 may be returning to the tank or may be delivered from the tank to other equipment such as fuel shut off mechanisms or for recirculation to carbon canisters or directly to engine fuel systems for combustion.

The wall 20 is preferably a multi-layer wall. The wall comprises an inner layer 24, an adhesive layer 26, a barrier layer 28, an adhesive layer 30, a regrind layer 32 and an outer layer 34. The barrier layer 28 may be manufactured from materials such as ethylene vinyl alcohol copolymer (EVOH) or other materials which substantially inhibit the passage of hydrocarbon vapour through the wall of the tank. The inner layer 24 may be selected from any material suitable for the purpose. This may include polyolefin, high density polyethylene, polyethylene, or other polymeric thermoplastic materials.

Where appropriate the inner layer may include additional substances such as carbon materials to provide some measure of electrical conductivity to assist in grounding the fuel tank. This is often desirable for ensuring that static electricity does not build up. Typically, in the prior art, the outer layer in tanks which have been made heretofore would be high density polyethylene. The material might be virgin material, or scrap, that is reground polyethylene material or combinations thereof. Where such materials are used as the outer layer of the tank, then in order to weld a hose fitting, there would need to be a high density polyethylene or similar material on the surface of the hose fitting which is to abut the tank wall.

In accordance with this invention, the material for the outer layer 34 is a modified polyolefin layer and is selected from a group of materials comprising materials which are compatible with the materials from which the hose fitting may desirably be made. The hose fitting 14 comprises a body portion 40. The body portion 40 is a substantially unitary structure which may be made from a single material, preferably in an injection molding procedure. The fitting 14 comprises a spigot portion 42. A passage 44 extends centrally through the fitting 40 to provide a passage for vapours from the aperture 22 along the passage 44 and exiting the end of the spigot 42. The spigot 42 advantageously comprises additional structural materials such as rib 46 adjacent the end of the spigot 42. The rib 46 or other such structure may be used for coupling a hose to the spigot 42. The rib 46 is illustrated merely by way of example. In the illustrated example, a hose can be pushed on the spigot 42 with the end of the hose passing over the rib 46. The hose clamp or the like can then be tightened around the hose and around the spigot 42 to make the necessary seal. Rubber o-rings or other seals can be also utilized as desired.

The body 40 of the fitting 14 comprises a surface 50 which is intended to bear against the wall 20 of the tank 12. The tank 12 comprises a surface 36 surrounding the aperture 22 which is approximately the same area as surface 50.

In order to join the fitting 14 to the tank 12, the fitting 14 is placed adjacent the outer layer 34 of the tank with the passageway 44 aligned with the aperture 22. The surfaces 50 and 36 are then heated. This may most conveniently be done by hot plate melting. In the hot plate melt procedure, the surface 50 and the surface 36 are heated simultaneously by a hot plate with the surface 36 touching one side of the hot plate and the surface 50 touching the other side. When the two materials are raised substantially near their melting point, the hot plate is removed and the two molten surfaces are brought into contact with the passage 44 registering with the aperture 22. Thermal fusion then occurs between the surface 50 of the fitting 14 and the surface 36 of the outer layer 34 to constitute a permanent vapour tight joint between the two components.

The fitting 14 is advantageously manufactured from a material which is suitable for its function. The material should have a creep strain (as defined in ASTM Test Method D2990, "Standard Test Methods for Tensile, Compressive, and Flexural Creep and Creep-Rupture of Plastics") which is less than the creep strain of the material of the outer layer. In addition, the material should have a tensile modulus of elasticity (as defined in ASTM Test Method D638, "Standard Test Method for Tensile Properties of Plastics") which is higher than the tensile modulus of the material of the outer layer. Such materials include polyamides including various types of nylon, glass reinforced polymeric materials and the like.

In order to provide the weld between the tank 12 and the fitting 14, the external layer 34 is manufactured from materials selected from the group consisitng of modified polyolefin materials, in particular, modified polyolefin with anhydride or acrylate functionality. Several brands of suitable resins are available from various suppliers. These include the adhesive resin developed by Mitsui Petrochemical Industries Limited and sold under the trade mark ADMER™. ADMER™ resins are said to bond to polyolefins, gas barrier resins and metals by thermal reaction. ADMER™ is a modified polyolefin which has functional groups which promote adhesion with different materials. These include polypropylene based resins as well as polyethylene based resins, as well as additional materials.

An additional material which has proved desirable is that sold by Union Carbide under the trade mark FLEXOMER™. Another material which has proved desirable is that sold by Uniroyal under the trade mark POLYBOND™.

The E.I. Dupont company markets resins which are suitable under the brands BYNEL™ and FUSABOND™. The modified polyolefin layer 36 of the tank 12 is mutually compatible with creep resistant materials as may be selected for manufacturing the fitting 14. If the fitting is made of polyamide, reinforced polyolefins or reinforced polyamides, it may be readily welded to the outer layer of modified polyolefin material. This provides a vapour tight weld between the tank and the hose fitting while at the same time providing a hose fitting which is sufficiently resistant to creep to enable the use of a hose clamp or the like to provide a vapour leak-free connection between the hose and the fitting. Thus, the fitting can be manufactured from materials which are typical for such fittings at this time, and in addition, may be welded to a plastic fuel tank with the outer modified polyolefin layer as described.

Claims

WE CLAIM:

1. A method of making a fuel tank system including a tank having a multilayer thermoplastic wall and a hose fitting comprising; selecting at least one barrier layer for inclusion in said multilayer thermoplastic wall of said tank, said barrier layer inhibiting passage of hydrocarbon vapour through said walls, said multilayer thermoplastic wall having an outer layer, selecting the material for said outer layer from the group consisting of modified polyolefins with anhydride and modified polyolefin with acrylate functionality, forming said hose fitting from a selected material, said selected material having a creep strain which is less than the creep strain of said material of said outer layer and a tensile modulus of elasticity higher than the tensile modulus of elasticity of said material of said outer layer, and welding said hose fitting to said outer layer of said tank.

2. A fuel tank system comprising a fuel tank and a hose fitting, said fuel tank comprising a wall, said wall comprising a plurality of layers of thermoplastic materials, said plurality of layers including at least one barrier layer for inhibiting passage of hydrocarbon vapours through said wall, said plurality of layers of said wall including an outer layer, said outer layer made from a material selected from the group consisting of modified polyolefin with anhydride and modified polyolefin with acrylate functionality, and said hose fitting made from a selected material, said selected material having a creep strain which is less than the creep strain of said material of said outer layer and a tensile modulus of elasticity higher than the tensile modulus of elasticity of said material of said outer layer.

3. The method of claim 1, wherein said tank comprises an aperture through said wall for passage of vapour and said fitting comprises a passage for passage of vapour and said fitting is welded to said tank with said passage registering with said fitting.

4. The method of claim 3 wherein said welding is produced by simultaneously heating a surface of said fitting and a surface of said tank.

5. The method of claim 1 wherein said material for said outer layer of said tank is selected from the group consisting of ADMER, FLEXOMER, POLYBOND, BYNEL and FUSABOND.

6. The method of claim 5 wherein said hose fitting is made from material selected from the group consisting of polyamide, nylons and glass reinforced polymeric materials.

7. The fuel tank system of claim 2, wherein the material of said outer layer of said wall is selected from the group consisting of ADMER,

FLEXOMER, POLYBOND, BYNEL and FUSABOND.