Fuel tank venting

Abstract: A fuel tank venting arrangement for a vehicle comprises a fuel tank (2) including at least two vent ports in its upper surface. Each vent port is provided with a rollover valve (4) and is in fluid flow communication with a back pressure control valve (12). The vent ports are connected together by a single manifold (16) which is secured to the tank (2) to form a fluid-tight seal.

Description: The present invention relates to a fuel tank venting arrangement for a motor vehicle. A vehicle fuel tank is vented to allow vapours to move in and out of the tank in order to keep internal pressure in the tank about equal to atmospheric pressure as fuel is drawn from the tank and as internal gas pressures build up. To reduce atmospheric emissions of fuel, vented vapours may be channelled via a back pressure control valve to a charcoal canister which absorbs and temporarily traps fuel vapour. On restarting the engine, filtered air flows through the canister and carries the fuel vapour away to be burned in the engine. The back pressure valve is used to prevent "trickle filling" of the fuel tank. The venting system typically comprises two vent ports, one on either side of the top of the fuel tank, both of which are connected to a back pressure valve by pipes. The back pressure valve is in turn connected to a charcoal canister. To prevent fuel from spilling out of the tank in the event of the vehicle turning over or banking steeply, each vent port is provided with a rollover valve ("ROV") which is welded to the tank or mounted by means of a grommet. A problem with such venting systems is that there are quite a number of places where leakage to atmosphere may occur, namely between each ROV and the tank, between each valve outlet and a pipe, and between each pipe and the back pressure valve. The cost of sophisticated connections to various components is high. It is an object of the present invention to reduce the above problem. According to an aspect of the present invention there is provided a fuel tank venting arrangement for a vehicle, comprising a fuel tank including at least two vent ports in its upper surface, each vent port being provided with a rollover valve and being in fluid flow communication with a back pressure control valve, characterised in that the vent ports are connected together by a single manifold which is secured to the tank to form a fluid-tight seal. The use of a single manifold reduces the number of potential fuel leakage points. Conventional ROVs and their attachments may be used but, because the manifold provides a barrier to the atmosphere, cheaper, less efficient, alternative valves and valve attachments could be used instead. The manifold may be formed to provide additional mounting brackets for other components if required. The use of the manifold is of particular cost benefit where severe evaporative emission requirements pertain, for example in the USA or as mandated under Stage 3 emission requirements in Europe. In such cases, the manifold may be co-extruded and/or formed from a fluorinated plastics material. The manifold may be secured to the tank by any suitable securing means. In a preferred embodiment the manifold is welded to the tank, but other securing means could also be used, for example a suitable adhesive. In a preferred embodiment, the manifold is formed from the same plastics material as the tank. The manifold is preferably blow moulded, preferably from polyethylene. For convenience hereinafter the invention will described with reference to a blow moulded polyethylene manifold which is welded to the tank; however it is to be understood that the invention is not limited to this embodiment. The manifold can be connected to the back pressure valve through a single outlet pipe, which may be integrally formed in the blow moulding process, or which may be subsequently welded to the manifold. Alternatively, the manifold may extend to encompass the back pressure valve, the manifold being welded or otherwise secured to the tank around or directly to the back pressure valve. This reduces the number of potential leakage points further. The invention will now be further described, by way of example, with reference to the following drawing in which: Figure 1 is a perspective view of a prior art venting arrangement in a known fuel tank; Figure 2 is a perspective view of a venting arrangement in a fuel tank in accordance with the present invention; and Figure 3 is a sectional view through part of the arrangement shown in Figure 2. The known fuel tank 2 shown in Figure 1 has two ROVs 4 mounted in vent ports on either side of the top of the tank, by means of grommets or welding. Each ROV 4 has an outlet tube 6 which is connected to a T junction 10 of a back pressure valve 12 by pipes 8. Leakage of fuel vapour can occur at any of the junctions between the tank 2 and the ROV 4, the ROV 4 and the pipe 8, and between the pipe 8 and the T junction 10. Referring now to Figures 2 and 3, identical parts are labelled with the same numbers as for Figure 1. A manifold 16, for example of blow moulded polyethylene, is secured to the upper surface of the tank 2 by means of hot plate welded joints 20 to form a fluid tight seal with the tank 2. The manifold 16 encloses both ROVs 4 so that any fuel vapour which escapes between the ROV 4 and the tank 2 will be contained within the manifold 16. This permits cheap or low technology tank attachment grommets 18 to be used to mount the ROVs. The manifold 16 is connected to an inlet pipe 14 on a back pressure valve 12 by a single pipe 8, via an outlet member 22. The back pressure control valve 12 is connected to a charcoal canister (not shown) which absorbs fuel vapours. The outlet member 22 is hot plate welded to the manifold 16 to provide a fluid tight seal, but could alternatively be formed as part of the manifold 16 during blow moulding. Use of the manifold 16 reduces the likelihood of fuel vapour escape to the atmosphere and permits the use of low cost mounting components for valves in the vent ports.

Claims: A fuel tank venting arrangement for a vehicle, comprising a fuel tank (2) including at least two vent ports in its upper surface, each vent port being provided with a rollover valve (4) and being in fluid flow communication with a back pressure control valve (12), characterised in that the vent ports are connected together by a single manifold (16) which is secured to the tank to form a fluid-tight seal. A fuel tank venting arrangement as claimed in claim 1, wherein the manifold (16) is made from the same material as the tank. A fuel tank venting arrangement as claimed in claim 1 or claim 2, wherein the manifold (16) is formed by a blow moulding process. A fuel tank venting arrangement as claimed in any one of the preceding claims, wherein the manifold is made of polyethylene. A fuel tank venting arrangement as claimed in claim 1, wherein the manifold is co-extruded. A fuel tank venting arrangement as claimed in claim 1, wherein the manifold is formed from a fluorinated plastics material. A fuel tank venting arrangement as claimed in any one of the preceding claims, wherein the manifold if formed to provide one or more mounting brackets for other components. A fuel tank venting arrangement as claimed in any one of the preceding claims, wherein the manifold extends to encompass the back pressure control valve. A fuel tank venting arrangement as claimed in any one of the preceding claims, wherein the manifold is welded to the upper surface of the tank.

Inventors: BOWLES DAVID THOMAS, BOWLES, DAVID THOMAS
Applicants: FORD MOTOR CO, FORD WERKE AG, GROUPE FORD FRANCE S A, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT, GROUPE FORD FRANCE S.A.
Application year: 1999
Main classification: B60K15
IPC codes: B60K15