GB2269373A

GB2269373A - Anti-trickle arrangement for a vehicle fuel tank

Info

Publication number: GB2269373A
Application number: GB9216871A
Authority: GB
Inventors: David Thomas Bowles
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1992-08-08
Filing date: 1992-08-08
Publication date: 1994-02-09
Also published as: GB9216871D0

Abstract

An anti-trickle arrangement for a vehicle fuel tank includes a float rollover valve 9 shrouded by a fuel impervious skirt 12 which extends into the tank 1 almost to the level 3 at which fuel is normally filled. Any attempt to trickle-fill the tank above the normal level causes the fuel to rise in the skirt 12 as the trapped air is vented through the vapour vent line 11. As the fuel rises further in the skirt 12 the float 9 is lifted to seal the vent line 11. This arrangement ensures that apart from the volume of the skirt, the air trapped in the remaining space 8 at the top of the tank remains and further filling will cause only overflow from pipe 6. A small orifice 16 towards the top of the skirt 12 allows fuel trapped in the skirt to escape slowly, when the filler pipe 6 is closed by a cover (Figure 3), until the float 9 of the rollover valve falls to open the vapour vent line 11 and permit normal operation of the rollover valve 9 as the vehicle is driven. The size of orifice 16 must be sufficiently small so as to allow the fuel to rise within the skirt preferentially over the fuel outside the skirt. <IMAGE>

Description

Anti-trickle Arrangement for a Vehicle Fuel Tank The invention relates to an anti-trickle arrangement for a vehicle fuel tank having a float rollover valve. Vehicle fuel tanks are generally fitted with a vapour vent line which allows for the vapour pressure within the fuel tank to be substantially equalised with the atmospheric pressure by venting excess gas into a vent line. Such vapour vent lines are generally fitted with a cut-off in the form of a float rollover valve. Such a valve will seal the tank from the vent line in the event of vehicle rollover. The valve is also adapted to prevent the tank from being overfilled when the fuel is introduced at a normal pump-flow rate. However, if the fuel flow rate is reduced to a trickle then the tank may be filled beyond the level normally set for cut-off.

It is desirable to prevent trickle filling of the fuel tank because this may result in premature closure of the rollover valve which would prevent any expansion of the contents of the tank, as a result of temperature changes, being released into the vapour vent line.

It is known from United States Patent No. 4,178,894 that a vehicle fuel tank may be provided with a buffer chamber which communicates with the interior of the tank only through a small fuel port at the bottom of the chamber and a small air vent communicating with a vapour vent line. The arrangement as described is not used with a rollover valve and the access to the vent line and to the buffer chamber to the tank is restricted.

According to the present invention there is provided an anti-trickle arrangement for a vehicle fuel tank including a float rollover valve controlling the flow of vapour from the tank to a vapour vent line, said arrangement having a fuel-impervious skirt which surrounds the rollover valve and extends into the tank almost as far as the normal full fuel level.

Preferably, the skirt is cylindrical and closely surrounds the rollover valve. The skirt may be provided with a small hole communicating the volume within the skirt to the vapour above the fuel in the tank.

The invention will now be described by way of example, with reference to the accompanying diagrammatic drawing in which: Figure 1 shows a cross section through a fuel tank with the fuel at its normal full level; Figure 2 shows a float rollover valve closed as the result of overfilling the tank; and Figure 3 shows the float rollover valve in its normal operating state with an overfull tank.

Referring to the drawings, Figure 1 shows a vehicle fuel tank 1 containing fuel 2 at the normal full level 3 determined by the point 4 at the bottom of the sensing tube 7. As fuel enters the tank from the fuel filler nozzle 5 which is inserted into the fuel tank filler pipe 6 the level of fuel rising in the tank initially expels vapour through the sensing tube 7 and out through the filler pipe 6.

However, when the fuel in the tank 1 reaches the point 4 and blocks off the vapour entry to the sensing tube 7, the remaining vapour is trapped in an expansion space 8 at the top of the tank adjacent to a rollover valve.

The fuel rollover valve comprises a float 9 and a cage 10 which normally permits vapour from the tank to flow into a vapour vent line 11. The passage of vapour from the space 8 at the top of the tank into the vapour vent line 11 permits the tank to be filled beyond its normal full level at a trickle rate depending upon the speed of vapour flow into the vent line 11. However because a space 8 at the top of the tank 1 is prevented from communicating with the vent line 11 when the fuel is at or above the level 13, there will always be some vapour trapped at the top of the tank even with the slowest rate.of trickle filling.

The rollover valve is surrounded by a substantially cylindrical fuel-impervious skirt 12. Referring now also to Figure 2, as the fuel is trickle fed from the nozzle 5 the fuel in the space 8 reaches the bottom of the cylindrical skirt 12. Only the vapour trapped within the skirt 12 can escape into the vent line 11. The level of fuel within the skirt 12 therefore rises until it reaches a level 14 when the float 9 closes the access to the vent line 11. If an attempt is made to further fill the tank it will only overflow from the pipe 6. Therefore when the float 9 closes the line 11 there is still a significant volume of vapour trapped in the expansion space 8 determined by the position of the point 4. The level of the fuel in the space 8 is initially determined by the level of the bottom of the skirt 12.However, as a small orifice 16 is located in the skirt 12, towards the top, adjacent to the cage 10, the fuel level within the skirt 12 is allowed to rise.

Referring now to Figure 3, if the filler pipe 6 is closed with a cap 17 it is desirable for normal operation of the vehicle that the float 9 of the rollover valve should be operating normally. It is therefore necessary for the float 9 to be unseated from the line 11, even after the tank has been overfilled by trickle filling. This is achieved by means of the orifice 16 which permits the level of fuel within the skirt 12 to drop to the level of the orifice 16 as shown. In this position the float drops to open the vent line 11 so that any expansion of fuel within the tank allows vapour to be vented into the line 11 in a normal manner.

Furthermore, as soon as the vent line opens, the fuel levels within and without the skirt 12 will equalise because they will both be subject to the same external pressure.

It will be appreciated that the size of the orifice 16 must be sufficiently small to allow the fuel to rise within the skirt 12 preferentially over the fuel outside of the skirt.

However, the orifice 16 must be sufficiently large to allow the fuel within the skirt 12 to flow out and so to cause the float 9 to fall which permits normal operation of the rollover valve as the vehicle is driven.

Claims

1. An anti-trickle arrangement for a vehicle fuel tank including a float rollover valve controlling the flow of vapour from the tank to a vapour vent line characterised in that a fuel impervious skirt shrouds the rollover valve and extends into the tank almost as far as the normal full fuel level.

2. An anti-trickle arrangement as claimed in claim 1 in which the skirt is substantially cylindrical.

3. An anti-tickle arrangement as claimed in claim 2 in which the cylindrical skirt closely surrounds the rollover valve so as to limit the volume within the skirt.

4. An anti-trickle arrangement as claimed in any preceding claim in which a small orifice towards the top of the skirt communicates the volume within the skirt to the vapour above the fuel in the tank.

5. An anti-trickle arrangement as claimed in claim 4 in which a vapour space is provided above the fuel in the tank which does not communicate with the vapour vent line when the tank is filled to the normal full fuel level.

6. An anti-trickle arrangement in a tank substantially as hereinbefore described with reference to the accompanying diagrammatic drawing.