GB2261639A

GB2261639A - Fuel tank shield

Info

Publication number: GB2261639A
Application number: GB9124726A
Authority: GB
Inventors: Ronald Pardy
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1991-11-21
Filing date: 1991-11-21
Publication date: 1993-05-26
Also published as: GB9124726D0

Abstract

In order to hinder permeation of fuel vapour through the walls of a plastics fuel tank 16, an external shield 20 is mounted around at least pan of the tank, with a seal 22 fitted between the tank and the shield to enclose a space 24 between the tank and the shield. <IMAGE>

Description

FUEL TANK SHIELD This invention relates to a shield for a plastics motor vehicle fuel tank. The invention is particularly intended to restrict permeation of fuel vapour through the walls of a plastic fuel tank.

The manufacture of motor vehicle fuel tanks from plastics, for example high density polyethylene, has many advantages.

However one of the disadvantages is that the plastics materials used are susceptible to permeation by fuel vapour from inside the tank. Since there are legal limits laid down to the amount of such permeation which is permitted, it is necessary in some cases to take steps to limit the permeation.

It is known to enhance the resistance of a plastics fuel tank to permeation by treating the surface of the tank with fluorine gas which changes the chemical structure of the surface plastic and radically reduces permeation. Other similar processes for chemically treating the surface of the plastic are known, but they all have the disadvantage that they are expensive.

it is also known, for example from DE-A-3 436 709, to coat the inner surface of a fuel tank with a thin metal layer to reduce permeation.

According to the present invention, there is provided a shield for a plastics motor vehicle tank, the shield being adapted to be mounted externally of the tank and spaced from the tank, and seal means for sealing the shield to the outer surface of the tank to provide an enclosed space between the tank and the shield.

The invention also provides a motor vehicle fuel tank installation in which the tank itself is of plastics material and where a shield is mounted externally of the tank and is spaced from the tank with a seal being mounted between the tank and the shield to provide an enclosed space between the tank and the shield.

The shield will extend around a substantial part of the external surface of the tank, so that any vapour which permeates through the shielded part of the tank will only permeate into the enclosed space and will then be trapped.

This will then produce a significant reduction in the quantity of vapour lost through permeation.

It is known from DE-A-3 822 620 and DE-A-3 824 582 to mount a heat shield adjacent to the external walls of the tank to protect the tank against heat from other vehicle components, typically from the exhaust pipe. In the constructions shown in these specifications, the space between the shield and the tank is unsealed and air and fuel vapour can flow freely around the surface of the tank.

Where a heat shield is required in any case for the reasons just described, the simple expedient of placing a seal between the heat shield and the tank can give the added benefit of permeation resistance.

The shield is preferably of metal. The seal may in itself be sufficient to support the shield, without any other shield supporting means being required. Alternatively however the shield may be supported by straps, brackets or other support means, with the seal being fitted between the shield and the tank, to enclose a space.

The enclosed space will normally contain a trapped volume of air, but under certain circumstances it may be advantageous to enclose a special atmosphere.

The invention will now be further described, by way of example, with reference to the accompanying drawing which is a cross section through part of a vehicle, showing a fuel tank partly cut away.

The Figure shows schematically at 10 the underside of a motor vehicle body. An exhaust pipe 12 is connected to a muffler 14. A plastics fuel tank 16 containing fuel 18 is supported beneath the body 10 by means which are not shown in the drawing. A shield 20 is fitted beneath the tank, and between the tank and the exhaust pipe/muffler assembly 12, 14.

As can be seen in the Figure that part of the shield 20 indicated at 20a provides protection for the tank against the heat generated by the exhaust pipe/muffler assembly 12, 14. That part of the shield indicated at 20b provides a permeation shield beneath the tank. The permeation shield area 20b is sealed to the external surface of the tank by means of seals 22. In practice there will probably be one continuous seal to enclose a space 24 between the tank and the shield.

In use, there will be some vapour permeation through the walls of the tank. The vapour which permeates through the lower walls of the tank will however collect in the space 24 and cannot escape from this space. The area covered by the shield will be chosen so that the amount of vapour which permeates through the uncovered area of the tank walls 16 will be within the limits allowed by regulation for vapour permeation.

The shield 20 will be made of a material which is conventionally employed as a shield in this situation. This will probably, but not necessarily, be a metal. Steel is likely to be an obvious choice. However aluminium or a plastic composite (possibly including aluminium foil) may also be appropriate.

The material of the seals 22 can conveniently be a closed cell polyurethane foam (EPDM).

Claims

1. A shield for a plastics motor vehicle tank, the shield being adapted to be mounted externally of the tank and spaced from the tank, and seal means for sealing the shield to the outer surface of the tank to provide an enclosed space between the tank and the shield.

2. A shield as claimed in Claim 1 which is of metal.

3. A motor vehicle fuel tank installation in which the tank itself is of plastics material and where a shield is mounted externally of the tank and is spaced from the tank with a seal being mounted between the tank and the shield to provide an enclosed space between the tank and the shield.

4. An installation as claimed in Claim 3, wherein the shield extends beyond the tank to provide a heat shielding function relative to an exhaust pipe.

5. An installation as claimed in Claim 3 or claim 4, wherein the shield extends substantially across the whole of the bottom of the fuel tank.

6. A shield substantially as herein described with reference to the accompanying drawing.

7. A motor vehicle fuel tank installation substantially as herein described with reference to the accompanying drawing.