GB2264107A - A float rollover valve for a vehicle fuel tank - Google Patents

Abstract

A float rollover valve 4 which vents vapour from a fuel tank when the fuel is below a predetermined level (Fig 1) but closes a vapour outlet orifice 2 when the fuel is above the predetermined level (Fig 2) also reacts to pressure build up within the tank to vent gas until the ambient pressure and the pressure within the tank are substantially equalised. This is achieved by using a weighted link 12 resting on a pressure sensitive member 14, eg a flexible wall of the tank, which moves downwardly when pressure builds up within the tank and so allows a flanged head 11 to act against detents 10 to draw a float 5 coupled to a plug 4 away from the gas vent orifice 2. This permits the fuel vapour and gas within the tank at a pressure P<3> to be vented through a tube 3 to the lower atmospheric pressure P<1>. In rollover conditions the orifice 2 is sealed by the plug 4 under the effect of a spring 9 and the gravitational effect on the float 5 (Figure 4). The float moves in a two part float chamber (6, 7, Figure 1) which has a reaction arm (8, Figure 1) against which the weighted link 12 bears in the rollover condition, the reaction arm passing through an aperture in the float 5. <IMAGE>

Description

Title: Float Rollover Valve for Vehicle Fuel Tanks Field of the Invention: The invention relates to float rollover valves for vehicle fuel tanks. The invention is particularly applicable to thin-walled fuel tanks particularly those made from plastics materials.

Background to the Invention: It is generally known to provide a cut-off valve mounted in a vehicle fuel tank so that when the fuel level reaches a predetermined level due to trickle filling, the valve closes a gas vent line in the top of the fuel tank to prevent liquid fuel spillage through the gas vent line. Such float valves may be arranged so that under accident conditions, if the fuel tank is inverted, the valve cuts-off automatically by providing a closure on the gas vent line regardless of the level of liquid within the tank.

A problem encountered with such valves is that pressure may build up within the tank when the valve is closed because of high fuel levels combined with changes of ambient temperature or atmospheric pressure which causes the pressure within the tank to increase relative to ambient pressure. This increase in tank pressure can adversely affect the metering of fuel to the engine of the vehicle, or cause fuel expulsion on cap removal.

The present invention seeks to overcome excessive pressure build up in a vehicle fuel tank.

Summarv of the Invention According to the present invention there is provided a float rollover valve for a vehicle fuel tank including a float directly coupled to a valve plug arranged to close a vent orifice and biased by gravity normally to rest on a member arranged to react to pressure build-up in the tank to lengthen the distance between the orifice and the member so that in u.se the valve is arranged to vent vapour pressure from the tank when the fuel is below a predetermined level within the tank, and arranged to seal the tank when the fuel is above the predetermined level providing that the ambient pressure difference within.the tank is below a predetermined pressure, and arranged to seal the tank in rollover conditions regardless of the ambient pressure difference.

In normal operation the invention is characterised in that pressure sensing means is provided to open the vent orifice when the fuel is above the predetermined level but the pressure in the tank, relative to ambient atmospheric pressure is above a predetermined pressure.

The pressure sensing means is preferably a weighted link resting on a flexible wall of the fuel tank which distorts under pressure to allow the weighted link to move under gravity and open the vent orifice so as to relieve the pressure.

The rollover valve may include a float which sinks in the fuel within the tank when inverted to operate the closure of the orifice.

Brief Description of the Drawings: The invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which:- Figure 1 shows a float rollover valve mounted in a vehicle fuel tank; Figure 2 shows the rollover valve in its closed position as a result of high fuel level to prevent excessive antitrickle; Figure 3 shows the valve opened as a result of pressure build up; and Figure 4 shows the rollover valve in the operational inverted position.

Specific Description of the Invention: Referring now to the drawings, figure 1 shows a float rollover valve mounted in an upper wall 1 of a vehicle fuel tank. The rollover valve is connected by way of an orifice 2 to a gas vent tube 3. The orifice 2 is arranged to be sealed by a plug 4 actuated by a float 5. The float is contained within a two-part float chamber having a first part 6 divided from a second part 7 by reaction arms 8 which extends through slots in a lower portion of the float 5. s The arms 8 support a helical spring 9 between the reaction arms 8 and the upper wall of the float 5. The slotted skirt of the float 5 is provided with detents 10 which cooperates with a flanged head 11 of a weighted link 12. The link 12 is constrained to move within guide walls 13 which form the lower end of the second part 7 of the float chamber.The end of the stem of the weighted link 12 rests on a flexible lower wall member 14 of the vehicle fuel tank. A stem 15 dependant from the bell of the float 5 is arranged to pass through the aperture between the reaction arms 8 and to rest on the flanged head 11 of the weighted link 12. This is the normal position of the rollover valve when the fuel within the tank is below the bell section of the float 5 as shown by surface 16 of the fuel in the tank.

The rollover valve is constructed as a two-part float chamber. During assembly the float 5 is located within the first part 6, the helical spring 9 is placed within the float 5. The second part 7 of the float chamber is loaded with the weighted link 12 and engaged with the outer wall of the first part of the float chamber so that spring clips 17 engage with an annular ring in the outer wall of the first part 6. The flanged head 11 is engaged within the lower slotted portion of the float 5 by springing it past the detents 10 on the skirt of the float 5.

In normal operation, the gas trapped above the surface 16 of the fuel in the tank is equalised in pressure relative to the ambient pressure by movement of vapour or air from inside to outside the tank, or vice versa as shown by the double headed arrows A1 and A2. The vapour within the fuel tank passes through ports 18 in the top of the first part 6 of the float chamber and vented via the gas vent orifice 2 and vent tube 3 to the atmosphere.

In operation, as the fuel level 16 rises air is trapped within the upper bell part of the float 5 and, as shown in figures 2, as the fuel level 16 continues to rise the float 5 rises from its rest position on the head 11 and the plug 4 seals the orifice 2. This prevents additional fuel from being forced into the tank. However if the level 16 rises as a result of temperature variation or if there is a pressure build up within the tank, then, when pressure difference between the ambient pressure P1 and the pressure within the tank P2 builds up the flexible lower wall member 14 to distorts and the distance between the upper and lower wall members of the tank increases. The weighted link 12 remains in contact with the member 14 and the flanged head 11 moves down until it engages the detents 10.As shown in figure 3 when the ambient pressure difference P1 minus P3 reaches a predetermined difference this causes the member 14 to flex from its normal position by a distance D and the weighted link 12 pulls the plug 4 from the orifice 2 permitting equalisation of the pressures within the fuel tank to the ambient pressure.

The pressure build up within the tank may be caused by excessive over filling, or, more generally, by changes in temperature or a reduction in the ambient pressure after the fuel tank has been filled sufficiently to close the gas vent. As the pressures equalise the gas trapped in the float 5 above level 19, as shown in figure 3, causes the plug 4 to once again engage the orifice 2 and seal the tank to prevent fuel escaping. The helical spring 9 has a spring rating sufficient to just support the weight support of the float 5 in contact with the flanged head 11 in the normal position when the plug 4 is not engaged with the orifice 2.

Figure 4 shows the valve inverted in the roll-over position.

It will be seen as no gas is trapped within the float 5 the weight of the float combined with the reaction of the helical spring 9 forces the plug 4 into the orifice 2 to seal the fuel tank and prevent fuel from escaping through the vent tube 3. It will be appreciated that any build up of pressure within the fuel tank in the rollover position does not affect the sealing of the orifice 2 as the weighted link 12 no longer has any effect on the float 5 and its end is disengaged from the member 14.

It will be appreciated that the rollover valve may be used in vehicle fuel tanks with rigid walls if the member 14 is formed by a pressure sensitive chamber, for example a sealed cylinder with concertina walls attached to the fuel tank below the weighted link 12. As the pressure builds up within the tank the concertina walls are compressed to lengthen the distance between the orifice 2 and the member 14 to permit the weighted link 12 to act against the detents 10 of the float 5. Any pressure build up within the tank in the inverted position will not release the plug 4 from the orifice 2 as the weighted link 12 is not directly coupled to the member 14.

It will be appreciated that other forms of pressure sensitive members maybe used to sense pressure build up within the fuel tank of a vehicle which may affect the metering of fuel and hence the performance of the engine.

It will also be appreciated that the equalisation of the pressure may not fully equate the pressure within the tank to the ambient pressure. However, the drop in pressure will be sufficient to reduce the pressurisation of the fuel in the tank so that the metering of the supply to the engine does not significantly affect the performance, or to prevent fuel ejection on cap removal.

Claims (5)

Claims

1 A float rollover valve for a vehicle fuel tank including a float directly coupled to a valve plug arranged to close a vent orifice and biased by gravity normally to rest on a member arranged to react to pressure build-up in the tank to lengthen the distance between the orifice and the member so that in use the valve is arranged to vent vapour pressure from the tank when the fuel is below a predetermined level within the tank, and arranged to seal the tank when the fuel is above the predetermined level providing that the ambient pressure difference within the tank is below a predetermined pressure, and arranged to seal the tank in rollover conditions regardless of the ambient pressure difference.

2 A float rollover valve as claimed in claim 1 in which the member consists of a weighted link which rests on a wall member of a pressure sensitive chamber which is arranged to react to pressure differences within the fuel tank relative to the ambient pressure.

3 A float rollover valve as claimed in any preceding claim in which a spring assists the float to close the valve plug during normal operation and in the rollover condition.

4 A float rollover valve as claimed in any preceding claim in which the float is mounted within a two-part chamber, the upper part of which is provided with ports through which gas may flow into a gas vent tube via the vent orifice.

5 A float rollover valve as claimed in claim 5 in which the lower part of the two-part chamber contain reaction arm which act as a guide for a stem within the float so that, in use, it is biased by gravity normally to rest on the member arranged to react to pressure build-up in the tank