GB2254846A

GB2254846A - A vent arrangement for a fuel tank

Info

Publication number: GB2254846A
Application number: GB9108432A
Authority: GB
Inventors: David Thomas Bowles; Anthony Alan Fitzgerald
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1991-04-19
Filing date: 1991-04-19
Publication date: 1992-10-21
Also published as: GB9108432D0

Abstract

A fuel tank 10 has a vent passage 18 through which fuel vapour can be vented from the tank. In order to close this vent passage during refuelling, a float valve 28 is arranged below the vent and inside a housing 24 with a skirt 32. When the fuel level rises to the maximum design level, fuel can still rise inside the skirt until the float shuts off the vent passage. A secondary valve 36 is movable to control flow between the inside and outside of the housing. Means such as a spring-biassed diaphragm 40 are provided to control the secondary valve 36. As described, valve 36 is closed during refilling soon after the float valve 28 closes, but is opened again when the filter cap is replaced and the fuel has been shaken up by movement of the tank. However if the tank orientation changes eg. due to a vehicle overturning, the spring moves so that the vent passage 18 is reclosed. <IMAGE>

Description

A VENT ARRANGEMENT FOR A FUEL TANK This invention relates to a vent arrangement for a fuel tank, in particular for a motor vehicle fuel tank.

Motor vehicle fuel tanks have to be fitted with a vent to prevent the tank either exploding or imploding due to changes in the internal tank pressure. The vent however has to be designed so that it closes automatically in the event of the vehicle turning over (so that fuel is not spilled), and so that the flow of gas or vapour out of the tank is at least restricted whilst the tank is being filled, to prevent overfilling.

It is known to use a float to close the vent when the fuel level in the tank rises. However this has the disadvantage that the float may be held in the 'vent closed' position by the tank internal pressure, even when the fuel level drops.

According to the invention, there is provided a vent arrangement for fitting in the top wall of a fuel tank, the arrangement comprising a housing which is open at the bottom to admit fuel, a vent passage through a top wall of the housing, a float valve member in the housing which can be moved by a rising fuel level to a position where it closes the vent passage, a second valve member in the wall of the housing which can open or close to permit or to prevent flow between the inside and the outside of the housing, and means for closing the second valve member during filling of the tank and for opening the second valve member at other times.

The open bottom of the housing will normally be positioned at the desired maximum fuel level in the housing. During filling, when the fuel level rises up to the maximum level, communication between the ullage space at the top of the tank and the vent will be cut off at the moment when the open bottom of the tank is blocked by the fuel. However the fuel level will still rise within the housing because the housing itself is vented. This rising fuel level will lift the float valve member to close the vent passage and when this has happened, no further fuel can be charged to the tank.

Because the vent passage will be completely closed, trickle filling of the tank will be impossible. The known expedient of having only a small diameter vent passage to discourage trickle filling will therefore be unnecessary, and a large diameter vent passage can be used.

The use of a housing with a depending skirt also helps to prevent any surges of liquid fuel from entering the vent passage.

When the second valve member is opened however, the column of fuel inside the housing will be subjected to the same pressure as exists in the rest of the ullage space, and the fuel level inside the housing will reach equilibrium with the level in the rest of the tank. The float valve member will drop and the vent passage will communicate with the interior of the tank, either by way of the second valve member or by way of the open bottom of the housing.

The means for closing the second valve member may be a diaphragm which is biased on one side by tank pressure and on the other side by atmospheric pressure. At the moment when the ullage space becomes closed, tank pressure rises sharply and will cause the valve to close. In a preferred form, atmospheric pressure reaches the other side of the diaphragm via a signal tube which leads into the top of the tank filler pipe. When the filler cap is off, the signal tube is open to atmospheric pressure, but when the cap is replaced the signal tube will be exposed to tank pressure so that the pressure on both sides of the diaphragm will be equal. A light spring can be provided to move the second valve member to the open position under these circumstances.

The float valve member and the housing are preferably designed so that they work together as a roll-over valve which closes the vent passage if the vehicle turns over.

The float may be supported by a spring. In the normal orientation of the arrangement, the mass of the float will hold the spring slightly compressed, and the vent passage will be open. If the vehicle turns on its side, or turns completely over, the energy stored in the spring will be sufficient to move the float to close the vent. The housing is preferably of constant cross-section so as to provide guide walls for the movement of the float.

The arrangement can be produced as a single plastics moulding which incorporates the housing, stub pipes to which vent and signal tubes will be connected and a valve seat for the second valve member.

According to a second aspect of the invention, there is provided a motor vehicle fuel tank incorporating a vent arrangement as set forth above. A signal tube may be connected between the second valve member and the top of the filler tube to provide the means for closing the second valve member during filling of the tank.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a motor vehicle fuel tank incorporating a vent arrangement in accordance with the invention; Figure 2 is a detail of part of the tank of Figure 1; Figure 3 is a cross-section through the tank of Figure 1 showing the tank full; Figure 4 is a detail of part of the tank of Figure 3; Figure 5 is a cross-section through the tank of Figures 1 and 3, showing the filler cap replaced; Figure 6 is a detail of part of the tank of Figure 5; and Figure 7 is an enlarged view of a vent arrangement in accordance with the invention.

Figure 1 shows a fuel tank 10 with a filler neck 12. The tank is in the process of being filled with fuel 22 dispensed by a fuel pump filler nozzle 14. A sensing tube 16 and a vent passage 18 are provided.

The height of the sensing tube entry to the tank internal cavity determines the maximum fuel level to which the tank should be filled. During filling, the air or vapour displaced from the tank will flow out through the filler neck 12 and through the sensing tube. Once the entry of the filler neck into the tank cavity is completely covered by the fuel, air/vapour can continue to escape through the sensing tube, but once the entry of the sensing tube is also covered, air/vapour can only escape through the vent tube 18.

Figure 3 shows the tank 10 filled to its maximum designed level. In this condition, an ullage space 20 exists above the liquid fuel.

As can be seen in Figure 2, a vent housing 24 is fitted in the top wall 26 of the tank 10. The housing contains a float 28 which normally sits in a lower position 30a in which air/vapour can flow from the tank, past the float and out through the vent passage 18. The housing has a skirt 32 which extends downwards into the tank, to a point substantially level with the top of the sensing tube entry at 34. The housing also has an opening at 36 for a second valve. The second valve has a valve member 38 connected to a diaphragm 40. One side of the diaphragm is exposed to the internal tank pressure; the other side of the diaphragm is exposed to the pressure in a signal tube 42. The diaphragm is also biased by a spring 44 which will open the valve when the pressures on both sides of the diaphragm are equal.

In use, starting with the tank 10 empty, the float 28 takes up the position 30a. Because the sensing tube 16 is unobstructed, the pressures at P1 and P2 (see Figure 1) will be equal and the secondary valve member 38 will be held open by the spring 44. The vent passage 18 will be unobstructed, but at this stage there will be little or no flow through the vent passage because the tank will be vented through the sensing tube 16 which has a much larger flow cross-section that the vent passage.

The state of the valves 28, 38 remains unchanged until the fuel level in the tank reaches its maximum. At this point, shown in Figure 3, the sensing tube 16 first becomes covered, so that the tank can no longer be vented through this route. At substantially the same time, the fuel level reaches the bottom of the housing skirt 32, so that the ullage space 20 cannot vent through the passage 18 either.

However the space within the skirt 32 and the housing 24 can vent through the passage 18, and as a result the level 25 (see Figure 4) in the housing will continue to rise. This will cause the float 28 to rise on the fuel surface to an upper position 30b until a valve surface 46 on the float engages in a valve seat 48 at the bottom of the passage 18.

Now the space within the housing 24 is no longer vented and any further fuel introduced into the filler neck 12 will only cause a rise in level in the filler neck itself.

Because the volume of air/vapour in the ullage space 20 is now trapped, and is subjected to the hydrostatic pressure arising from the head of fuel in the filler pipe, the pressure P1 will rise above atmospheric. P2 still represents atmospheric pressure, because the mouth of the filler neck is still open. Therefore P1 > P2 and the secondary valve 38 will close.

Figures 5 and 6 show what happens when the filler cap 50 is replaced. In this situation, a second trapped air/vapour volume exists at 52. When the vehicle is in motion and the fuel is shaken up, the pressures P1 and P2 will equalise.

The secondary valve 38 will then be opened by the spring 44 and the pressure above the fuel in the housing 24 will equalise with the pressure in the ullage space 20, so that the fuel levels come to equilibrium. The float 28 will then fall within the housing 24 so that the vent passage is open and can carry out its function of venting the tank during running, while the filler cap is closed.

It will be noted that the valve seat 36 for the secondary valve is above the maximum liquid fuel level 25 in the housing 24, so that the vapour pressures inside and outside the housing will equalise as soon as the secondary valve is opened.

Figure 7 shows some constructional detail. A hole 54 is made in the top wall 26 of the tank, and the housing 24 is placed through this hole. The housing has an external flange 56 which is sealed around the edge of the hole. If both the tank wall and the housing are of plastics materials, then this joint can be achieved by welding the two together.

The float valve member 28 is supported by a spring 58 against a ledge 60 inside the housing. In the upright position shown, the weight of the valve member itself will compress the spring 58 so that the valve member takes up the position shown in Figure 7. However if the orientation of the housing changes, perhaps because the vehicle in which the tank is installed has turned on its side, then the spring will move the valve member to close the vent passage 18, and this movement will be reinforced by the weight of any liquid fuel entering the housing 24 or by vapour pressure which will act on the back of the float valve member.

Figure 7 also shows an alternative location for the secondary valve member.

The arrangement described thus provides, in a single housing, a way in which the vent passage 18 can be kept open at the times during which it should be kept open, and can be closed automatically as the tank is being filled to its maximum level.

Claims

1. A vent arrangement for fitting in the top wall of a fuel tank, the arrangement comprising a housing which is open at the bottom to admit fuel, a vent passage through a top wall of the housing, a float valve member in the housing which can be moved by a rising fuel level to a position where it closes the vent passage, a second valve member in the wall of the housing which can open or close to permit or to prevent flow between the inside and the outside of the housing, and means for closing the second valve member during filling of the tank and for opening the second valve member at other times.

2. A vent arrangement as claimed in Claim 1, wherein the means for closing the second valve member is a diaphragm which is biased on one side by tank pressure and on the other side by atmospheric pressure.

3. A vent arrangement as claimed in Claim 2, wherein atmospheric pressure reaches the other side of the diaphragm via a signal tube which leads into the top of the tank filler pipe.

4. A vent arrangement as claimed in Claim 2 or Claim 3, wherein a spring is provided to move the second valve member to the open position when the pressures on both sides of the diaphragm are equal.

5. A motor vehicle fuel tank having a top wall and a vent arrangement fitted in the top wall, the arrangement comprising a housing which is open at the bottom to admit fuel, a vent passage through a top wall of the housing, a float valve member in the housing which can be moved by a rising fuel level to a position where it closes the vent passage, a second valve member in the wall of the housing which can open or close to permit or to prevent flow between the inside and the outside of the housing, and means for closing the second valve member during filling of the tank and for opening the second valve member at other times.

6. A fuel tank as claimed in Claim 5, wherein the open bottom of the housing is positioned at the desired maximum fuel level in the housing.

7. A fuel tank as claimed in Claim 5 or Claim 6, wherein the float valve member and the housing are designed so that they work together as a roll-over valve which closes the vent passage if the vehicle turns over.

8. A fuel tank as claimed in Claim 7, wherein the float is supported by a spring.

9. A vent arrangement as claimed in any one of Claims 1 to 4, in the form of a plastics moulding which incorporates the housing, stub pipes to which vent and signal tubes will be connected and a valve seat for the second valve member.

10. A fuel tank as claimed in any one of Claims 5 to 8, wherein the vent arrangement is in the form of a plastics moulding which incorporates the housing, stub pipes to which vent and signal tubes will be connected and a valve seat for the second valve member.

11. A vent arrangement substantially as herein described with reference to the accompanying drawings.

12. A fuel tank substantially as herein described with reference to the accompanying drawings.