GB2246769A - A fuel tank for liquid fuel for an internal combustion engine - Google Patents

Abstract

A fuel tank-for liquid fuel for an internal combustion engine subject to orientation changes in normal use, having a flexible membrane 27 which allows changes in volume, within a rigid casing 11. The latter has a sealable fuel filler inlet (15) and a breather valve or opening 26 allowing the ingress and/or egress of air to the rigid casing 11 outside the volume enclosed by the membrane 27. A fuel outlet duct 19 has a flexible dip tube 20 extending within the flexible membrane and provided at its inlet end with a filter 25 and means (38, 39 & 40, fig 5) for preventing obstruction of the inlet opening 36 thereof by the flexible membrane 27 when in its collapsed state. A resilient element 29 may be interposed between the rigid casing and flexible membrane, to allow the membrane to expand without over stressing the casing. The membrane can be in the form of a sac secured to the outlet duct and filler opening or it can be trapped between the two parts of the casing by its periphery, (fig 4). <IMAGE>

Description

A FUEL TANK FOR LIOUID FUEL FOR AN INTERNAL COMBUSTION ENGINE The present invention relates generally to an improved fuel tank for liquid fuel for an internal combustion engine, and to an internal combustion engine having such a fuel tank.

Portable internal combustion engines subject to orientation changes in use, such those used for chain saws, brush cutters, angle grinders and other such machines are currently exposed to a fire risk which although not great nevertheless exists. The fire risk arises from the necessity of providing a breather opening to the fuel tank to allow the volume of gas within the tank to expand or contract either with temperature changes or as the fuel is withdrawn from the tank so that there are no operating difficulties due to the pressure differential between atmospheric pressure and the pressure to which the fuel is subject, and which would cause erratic running.

Conventionally, such breather openings on valves are fitted in the fuel tank filler cap or tank wall. The fuel tanks of internal combustion engines which are not subject to orientation changes experience no difficulty in this connection since they can be fitted at a suitable level, perhaps by the use of a duct or tube extending above the level of the tank, at a point higher than any which the fuel would reach in normal use. A simple opening, therefore, suffices to allow the escape of any gas under super atmospheric pressure or the intake of air as the fuel is withdrawn.Since the gas escaping from the fuel tank upon, for example, thermal expansion due to warming of the contents may contain vaporised fuel arrangements are sometimes made to direct this to a safe location, for example by a duct leading to the inlet manifold of the engine so that any fuel vapour can be entrained with the inducted air for combustion in the engine.

Such a situation is not practical, however, in the case of portable internal combustion engines such as those referred to briefly above, since they may be required to operate from time to time in an orientation other than a straightforward upright orientation. For example, a chain saw engine may spend a major part of its working life turned through an angle of 900 from its upright orientation, in which latter position the blade lies in a vertical plane, since in most cases it is necessary to make horizontal cuts through the trees to be felled. when lopping branches it is sometimes necessary to invert the chain saw altogether.The withdrawal of fuel from a fuel tank in such an engine is achieved by means of a fuel delivery pipe having a flexible dip tube which is weighted so that the inlet end always falls under the action of gravity to the lowermost part of the tank in whatever orientation it may be found at the time, so that it remains below the surface of the fuel even if the tank is only partly full, and consequently fuel is delivered to the engine at all times in any orientation. If an orientation change results in the breather valve or opening being located below the surface of the fuel, however, a certain amount of leakage takes place at least by capillary action, and this small quantity of leaked fuel then spreads over the outside of the engine and constitutes a fire risk should it for any reason be subject to ignition.

The need for a breather opening of some form cannot be avoided, since the fuel delivery system must be maintained in pressure equilibrium with the atmosphere if the engine is to operate satisfactorily in all orientations, and the option of omitting this breather is therefore not available.

The present invention seeks, therefore, to provide a fuel tank for the liquid fuel of an internal combustion engine which will be entirely secure against leakage, but will nevertheless provide an appropriate breather to equalise the pressure within the tank with atmospheric pressure experienced at the carburettor or fuel injection system of the engine.

According to one aspect of the present invention, therefore, a fuel tank for liquid fuel for an internal combustion engine subject to orientation changes in normal use, has a flexible membrane within a rigid casing in which the membrane has a sealable fuel filler inlet and a breather valve or opening allowing the ingress and/or egress of air to the rigid casing outside the volume enclosed by the membrane, and a fuel outlet duct having a flexible dip tube extending within the flexible membrane and provided at or adjacent its inlet end with means for preventing obstruction of the inlet opening thereof by the flexible membrane when in its collapsed state.

By this means the partial or total collapse of the membrane as fuel is withdrawn from the tank will not detract from the free flow of fuel through the inlet of the dip tube regardless of the orientation of the tank until all of the fuel has been completely withdrawn from the tank (apart from any residual pooling).

In one embodiment of the invention the flexible membrane is in the form of a sac sealed around the mouth of the fuel filler opening. Alternatively, however, the flexible membrane may be secured around its periphery to the rigid casing, in which case it may be shaped so as to follow, at least approximately, the contours of the rigid casing when the tank is completely full and/or when the tank is completely empty.

In such a construction the periphery of the flexible membrane may be secured in place in any one of a number of ways. For example, the membrane may be trapped between two parts of the rigid casing, which may be made as half shells, or maybe secured in place by a suitable fixing member or band appropriately secured to the rigid casing.

The flexible dip tube of the fuel delivery duct may be sealed to the rigid casing and the flexible membrane sealed around the delivery duct connector by which it is secured to the rigid casing. This latter construction is particularly suitable for a sac-type embodiment. In an embodiment in which the membrane is secured around its periphery to the rigid casing, it is possible to position both the breather opening and the fuel delivery duct connection directly to the rigid casing (obviously on opposite sides of the membrane) in which case conventional sealing means between the connector and the rigid casing may be employed.

The inlet opening of the fuel delivery duct flexible dip tube may be surrounded by a filter releasably fitted to the inlet end of the said flexible dip tube, and the said means for preventing obstruction of the inlet opening of the flexible dip tube by the flexible membrane when in its collapsed state may include members operative to maintain the membrane spaced at least a minimum distance from the said opening and/or the said filter.

In a preferred embodiment of the invention the said means for preventing obstruction of the inlet end of the flexible dip tube 6f the fuel delivery duct includes a cover or cage of shaped elongate members the form of which is such as to hold the flexible membrane spaced from the open end of the dip tube and/or the inlet to the filter when the membrane is in its collapsed state whereby to leave the said open end of the dip tube and/or inlet to the filter in communication with the liquid within the enclosure defined by the membrane.

Such cover or cage preferably comprises a plurality of rectilinear bars defining a generally cylindrical nominal surface. In addition , or alternatively, there may be provided or further provided one or a plurality of projecting members extending axially and/or radially over the generally cylindrical surface defined by a filter.

The flexibility of the membrane allows it to collapse progressively as the fuel is withdrawn from the tank so that the volume enclosed by the membrane is always totally filled with liquid. In addition to the volume changes of the membrane within the rigid casing to accommodate withdrawal of fuel, it is also necessary to take account of possible volume increases due to thermal expansion. This can be accommodated, when the tank is part full, by the flexibility of the membrane itself, since this can clearly adapt its shape to larger as well as to smaller volumes up to the maximum volume defined by the interior of the casing.In order to take account of the one further possibility, that the tank may be completely filled with fuel at a low temperature, for example, by drawing it from an underground container on a hot day, so that after having filled the tank the fuel may increase in volume by thermal expansion, the present invention incorporates the additional feature of means for defining the normal maximum volume of the enclosure defined by the membrane to be less than the volume determined by the casing at atmospheric pressure. this can be achieved, for example, by the provision of a resilient element interposed between the rigid casing and the flexible membrane. The resilience of such member will not be overcome at atmospheric pressure by the mass of the liquid.However, if the pressure within the liquid increases after the tank has been sealed shut in completely full conditions the resilient member may compress to allow volume changes and thereby relieve the outer casing from any excess pressure which might otherwise be exerted due to the fact that, in such circumstances, the breather opening is effectively sealed by the membrane.

The present invention also comprehends an internal combustion engine having a fuel tank as defined hereinabove.

Various embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic sectional view of the first embodiment of the invention showing the tank full in normal conditions: Figure 2 is a similar schematic sectional view of the embodiment of Figure 1 showing the tank partly empty: Figure 3 is a schematic sectional view of the embodiment of Figures 1 and 2 showing the tank completely full and at the super-atmospheric pressure: Figure 4 is a schematic sectional view of an alternative embodiment illustrating the tank in an almost empty condition: and Figure 5 is a perspective view of a fuel filter head suitable for attachment to the end of the dip tube.

Referring now to the drawings, it will be appreciated that the tank illustrated is shown only schematically as a rectangular casing whereas, in practice, a shaped casing for accommodation of the outline of the particular internal combustion engine or machine powered thereby is more usual.

The rigid fuel tank casing is generally indicated with reference 11 and comprises two half-shells generally indicated 12, 13 joined along a junction line 14 by any suitable known technique. For example, if the rigid casing half shells 12, 13 are made of plastics (as is often the case) the junction 14 may be effected by welding.

The first half shell 12 has an opening 15 defined by an enlarged surrounding rim 16 for receiving a filler cap (not shown) and an opening 17 for fuel delivery, which houses a fuel delivery coupling 18 interconnecting an external fuel delivery line 19 and an internal fuel delivery line dip tube 20. In the embodiment illustrated the connector 18 has an internal flange 21 and a threaded body passing through the opening 17, onto which is screwed a threaded lock nut 10 to retain the connector 18 in position. Externally the connector 18 has a spigot 22 over which the fuel delivery line 19 is fitted and to which it may be secured in a fluidtight sealed fashion by means of a suitable clamp.

Within the tank 11 the connector 18 has an internal spigot 23 over which one end of the fuel delivery line dip tube 20 is fitted, and this likewise may be secured in position by a clamp or may rely on the resilience of the fuel delivery line dip tube 20 to retain it in position.

At its free end 24 the fuel delivery line dip tube 20 is fitted to a fuel filter head 25 the construction of which will be described hereinbelow with reference specifically to Figure 5. The fuel filter head acts as the inlet to the dip tube 20 and has sufficient mass to ensure that, taking into account the resilience and flexibility of the dip tube 20, and the fact that the tank 11 is intended to adopt any orientation during normal use, the dip tube inlet end 24 can be positioned at the lowermost part of the tank entirely within any liquid contained therein which, likewise, will adopt a position at the lowermost part of the tank regardless of its orientation.

The second half shell 13 of the rigid casing has an opening 26 which constitutes the breather opening as will be described hereinbelow. Within the rigid casing constituted by the two half shells 12, 13 is located a flexible membrane 27 which has an annular mouth 28 engaged within the opening 15 in the casing shelf half 12 and is sealed such as by welding around the flange 21 of the delivery tube connector 18. Apart from these two features the flexible membrane 27 is in the form of a totally enclosed sac. Between the membrane 27 and the casing shell half 13 is located a foam resilient pad 29 which has a smoothly rounded convex surface presenting no sharp asperities to the membrane 27.In the condition illustrated in Figure 1, with the tank completely filled at normal atmospheric pressure, the pad 29 is uncompressed and offers a residual volume for expansion, by compression, as illustrated in Figure 3. The situation may arise, for example, if cold fuel is used to fill the tank completely on a warm day. After a short period in a such circumstances the fuel temperature rises and the associated thermal expansion could result in stresses on the rigid casing 12, 13 greater than its bursting strength. In conventional tanks, of course, such thermal expansion results in nothing worse than leakage through the breather opening, but in the present case the breather opening 26 is sealed by the membrane 27 when the tank is completely filled.As fuel is withdrawn from the tank through the delivery line 19 the membrane 27 can gradually collapse with air being drawn into the space within the casing 12, 13 outside the membrane 27 through the breather opening 26. No valve or other restrictor is required for the breather 26, which can be merely a plain hole as illustrated in the drawings. As the membrane 27 collapses further, with the continued withdrawal of fuel from the tank, the risk of it closing over the opening to the dip tube and thereby starving the engine of fuel is resisted by the guard means around the filter which will be described in relation to Figure 5. It is sufficient to appreciate, at this point, that however full or empty the fuel tank is the membrane holds the fuel in an enclosed volume immediately surrounding the filter head 25 so that, regardless of the orientation of the tank 11, fuel can be withdrawn through the fuel delivery line 19 without obstruction.

Figure 4 illustrates an alternative embodiment having many features in common with that of the embodiments of figures 1 to 3, but differing in that the membrane is in this embodiment shaped as a cup 31 having a peripheral rim 30 sealed between the two rigid casing half shells 12, 13. In Figure 4 the tank is shown in an almost empty condition.

Turning now to Figure 5, the filter head 25 comprises a body having two terminal circular flanges- 32, 33 holding between them a cylindrical porous filter element 34 within which is located the inlet tube 35 having an elongate opening 36.

The fuel inlet 36 leads to a spigot 37 off the filter head 25 over which the free end 24 of the flexible dip tube 20 is fitted.

Around the cylindrical surface defined by the filter element 34 is fitted a ribbed cage comprising a plurality of elongate rectilinear circumferentially spaced cage bars 40 which project radially inwardly of the circular supports 38, 39. The rectilinear bars 40 hold the flexible membrane 27 away from the filter head so that fuel can flow between the bars into the filter. Should the membrane 27 entirely wrap the cylindrical surface defined by the bars 40, fuel can still flow into the filter inlet 25 through the circumferentially spaced openings at the ends of the filter head defined by the radial separation between the terminal discs 32, 33 off the filter support and the circular support members 38, 39 between the ends of the ribs 40. The only circumstances in which the membrane 27 can wrap itself sufficiently tightly around the cage defined by the ribs 40 to obstruct every individual space between each adjacent pair of ribs 40 as well as enclosing the end gaps 41 at both ends of the filter head 25 is when there is no fuel left in the tank.

Claims (15)

1. A fuel tank for liquid fuel for an internal combustion engine subject to orientation changes in normal use, having a flexible membrane within a rigid casing which latter has a sealable fuel filler inlet and a breather valve or opening allowing the ingress and/or egress of air to the rigid casing outside the volume enclosed by the membrane, and a fuel outlet duct having a flexible dip tube extending within the flexible membrane and provided at or adjacent its inlet end with means for preventing obstruction of the inlet opening thereof by the flexible membrane when in its collapsed state.

2. A fuel tank as claimed in Claim 1, in which the flexible membrane is in the form of a sac sealed around the mouth of a fuel filler opening.

3. A fuel tank as claimed in Claim 1 in which the flexible membrane is secured around its periphery to the rigid casing and is shaped so as at least approximately to follow the contours of the rigid casing when the tank is completely full and/or when the tank is completely empty.

4. A fuel tank as claimed in Claim 3, in which the periphery of the flexible membrane is trapped between two parts of the rigid casing.

5. A fuel tank as claimed in any preceding Claim, in which the flexible dip tube of the fuel delivery duct is sealed to the rigid casing and the flexible membrane is sealed around the delivery duct connector by which it is secured to the rigid casing.

6. A fuel tank as claimed in any preceding Claim, in which the inlet opening of the fuel delivery duct flexible dip tube is surrounded by a filter releasably fitted to the inlet end of the said flexible dip tube.

7. A fuel tank as claimed in any preceding Claim, in which the means for preventing obstruction of the inlet end of the flexible dip tube of the fuel delivery duct includes a cover or cage of shaped elongate members the form of which is such as to hold the flexible membrane spaced from the open end of the dip tube when wrapped around it so as to leave the said open end of the dip tube in communication with the liquid within the enclosure defined by the membrane.

8. A fuel tank as claimed in Claim 6 or Claim 7, in which the said cover or cage comprises a plurality of rectilinear bars defining a generally cylindrical nominal surface.

9. A fuel tank as claimed in Claim 8, in which there are further provided one or a plurality of projecting members extending axially and/or radially of the generally cylindrical surface defined by the said cage bars.

10. A fuel tank as claimed in any preceding claim, in which there are further provided with means for accommodating an increase in the volume of fuel within the tank.

11. A fuel tank as claimed in Claim 10, in which the said means for accommodating expansion comprise means for defining the normal maximum volume of the enclosure defined by the membrane to be less than the volume determined by the casing at atmospheric pressure.

12. A fuel tank as claimed in Claim 11, including a resilient element interposed between the rigid casing and the flexible membrane.

13. A fuel tank as claimed in any of Claims 6 to 12, in which the said cover or cage is removable to permit exchange and/or cleaning of the filter.

14. A fuel tank substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

15. An internal combustion engine having a fuel tank as claimed in any preceding Claim.