Fluid handling – Control by change of position or inertia of system – Vent opening or closing on tipping container
Reexamination Certificate
2000-06-06
2001-09-18
Rivell, John (Department: 3753)
Fluid handling
Control by change of position or inertia of system
Vent opening or closing on tipping container
C137S202000, C137S587000, C251S144000
Reexamination Certificate
active
06289915
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to fluid systems and more particularly to controlling emissions through attachments in multi-layer plastic vessel fluid systems.
BACKGROUND
Fuel tanks for motorized vehicles have been used for many years. Typical fuel tanks are box-like, rectangular or cylindrical in shape and can contain from 10 to 30 gallons or more of a liquid fuel. Most of the current fuel tanks installed in motorized vehicles today are typically plastic or metallic in nature. However, fuel may be lost through joints between metal sections, from an instrument sensor port, from the fuel line leading to and from the engine, or from the fuel neck during refueling procedures. Further, in the case of plastic tanks, fuel may be lost through the plastic itself.
Recently, improvements to fuel tank technology have been directed to the manufacture of fuel tanks from thermoplastic, composite, or thermosetting materials using a variety of laminate or composite structures. One problem arising from the use of such materials in a fuel tank relates to increased permeability of fuel when compared to metal tanks.
To decrease the emission of fuel from these plastic tanks, improvements have focused on adding barrier layers resulting in tanks having multilayer walls. For example, U.S. Pat. No. 3,616,189 to Harr teaches an improved container having multiple layers including a nylon barrier film. However, the manufacture of multilayered or laminate materials often involves complex, expensive processing steps and expensive materials.
Another way to improve barrier properties of multi-layer structures involve adding specific chemical barrier materials to the surface of tanks or to the thermoplastic compositions used to make the tanks. For example, Walles, U.S. Pat. No. 3,740,258 and Shefford, U.S. Pat. No. 4,371,574 teaches that the addition of sulphonic acid or sulphonate groups on the surface of tank materials can improve barrier properties. Further, Wood, U.S. Pat. No. 5,928,745 adds a cyclodextrin barrier additive to a thermoplastic material used in at least one layer of a multi-layer thermoplastic fuel tank. While many of these systems improve barrier properties, significant improvements may still be achieved.
While the above solutions have improved the barrier properties of multi-layer fuel tank systems, these systems do not address the residual permeation problems occurring at attachment regions on the tank. Fuel or fuel vapor may escape through leak paths between layers of the plastic fuel tank or along exposed surfaces between the attachments and the overmolding.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to exploit the swelling properties in overmolded attachments to a multilayer fuel tank to close possible leakage paths at the interface between the different materials making up the overmolded attachments.
It is another object of the present invention to exploit the barrier properties of the materials used in overmolded attachments to increase the length of the diffusion path for the hydrocarbon molecules.
The above objects are accomplished by redesigning the overmolded components in four ways. First, cavities or grooves are added to the design of the barrier portion of the multilayer design, allowing the high-density polyethylene overmolding to swell within the cavity or groove and close the leak path at the interface between the two materials.
Second, the polyethylene overmolding in the area corresponding to the tank wall is molded conical rather than cylindrical so as to create a weld between the conical portion of overmolding material and the tank wall. This ensures that no gaps will exist between the tank wall and the attachment.
Third, the diffusion path of hydrocarbon molecules within the high density polyethylene overmolding is lengthened to decrease the permeation of hydrocarbon molecules through the attachment.
Fourth, barrier cores are added to the foot of the attachment to generate compressive stresses in the polyethylene layer to press the polyethylene layer against the barrier layer to further interrupt any leak path in these regions. This presence of barrier cores provides some additional protection against permeation.
Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings.
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Nulman Mark
Rossi Giuseppe
Kajander John E.
Rivell John
Visteon Global Technologies Inc.
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