GB2168300A

GB2168300A - Vehicle fuel tank venting system

Info

Publication number: GB2168300A
Application number: GB08431385A
Authority: GB
Inventors: Ronald Peter Pardy
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1984-12-12
Filing date: 1984-12-12
Publication date: 1986-06-18
Also published as: GB8431385D0; GB2168300B

Abstract

A vehicle fuel tank vent system 21 has a vent tube 22 with a vent valve 28 opened by an excess pressure in the tank 10 sufficient to prevent "trickle filling". A by-pass tube 30 provides for entry of air into the tank 10 when fuel is drawn from the tank by the vehicle fuel system. A sensing tube 16 determines a maximum fuel level 18 for the tank and establishes the tank ullage space 20. <IMAGE>

Description

SPECIFICATION Vehicle fuel tank venting system This invention relates to fuel tank systems for vehicles.

Many motor vehicles have a fuel tank with a filler pipe communicating with the fuel tank below an ullage space and a sensing tube connected to the upper end of the filler pipe. The lower end of the sensing tube communicates with the interior of the tank and defines the lower level of the ullage space.

When a tank of this kind is filled, air/vapour escapes through the sensing tube until the fuel level reaches the lower end of the sensing tube. The fuel then fills the filler pipe until it reaches the filling nozzle and (assuming the normal kind of nozzle is being used) cuts off further supply of fuel.

It is preferable to fit a non-vented filler cap and arrange for venting of the ullage space to allow for withdrawal of fuel from the tank or expansion of fuel into the ullage space. It is a well-known problem with systems of this kind that the ullage space can be "trickle filled" by allowing the level of fuel in the filler pipe to fall as air/vapour exits slowly through the venting system.

It is known (see for example German patents 2046562 and 2752645) to close the vent system by a valve actuated by removal of the filler cap or the opening of a flap covering the filler cap. The vent system is thereby closed whenever the fuel tank is being filled so that the ullage space cannot be "trickle filled" but operates normally to vent the tank as soon as the filler cap has been replaced or the flap closed. This arrangement solves the prob lem but is somewhat expensive and can leave the tank unvented if a non-standard filler cap is used or if the flap is accidentally left open.

The present invention seeks to prevent "trickle filling" without the use of such a valve.

According to the invention we provide a vehicle fuel tank system of the kind described above characterised in that the venting means (21) includes: a valve (28) which can be opened only by a pres sure in the tank (10) sufficient to maintain a head of fuel (A) in the filler pipe (12) and thereby prevent further filling of the tank (10) after the fuel level reaches the lower end of the sensing tube (16).

The invention will now be described with refer ence to the accompanying drawings in which: Figure 1 is a sectional view of a vehicle fuel tank system embodying the invention; and Figure 2 is an enlarged view of the circled portion of the fuel tank system of Figure 1.

A fuel tank 10 adapted to be mounted at the rear of a motor car (not shown) has a filler pipe 12 con nected at its lower end to the fuel tank 10. A filler cap 14 of the non-venting type is mounted on the upper end of the filler pipe 12.

A sensing tube 16 communicates with the upper end of the filler pipe 12 and extends into the fuel tank 10 to define a normal maximum fuel level 18 and an ullage space 20.

A venting system 21 includes a vent tube 22 which extends through the highest part of the fuel tank 10 to a reservoir 24. The upper part of reservoir 24 is vented to atmosphere by a downwardly extending tube 26.

A check valve 28 in the vent tube 22 below the reservoir 24 comprises a ball 34 cooperating with a seat 32. The weight of the ball 34 is such that it is unseated by a pressure in the tank 10 equivalent to a head of fuel approximately equal to the height of the filler cap 14 above the minimum fuel level 18.

A by-pass tube 30 connects the vent tube 22 intermediate the venting valve 28 and the reservoir 24 to the interior of the tank 10 below the maximum fuel level 18 at a location remote from the filler pipe 12.

In operation the fuel tank 10 can be filled through the filler pipe 12 until the level of fuel in the fuel tank 10 reaches the lower end of the sensing tube 16. The normal exit of air/vapour from the fuel tank 10 is then cut-off and fuel quickly fills the filler pipe 12 to reach the filler nozzle and shut off the supply of fuel.

The lower end of the by-pass tube 30 is below the fuel level. Air/vapour can vent only through the vent valve 28 if the pressure in the tank 10 that which would maintain the head of fuel A in the filler pipe 12. Thus the venting valve 28 prevents venting of the ullage space during filling, thereby preventing overfilling above the maximum fuel level 18.

When the filler cap 14 has been replaced, air is drawn into the fuel tank 10 via the by-pass tube 30 as soon as fuel is taken from the fuel tank 10 by the vehicle fuel system (not shown).

Expansion of the fuel after filling causes air/vapour pressure to rise above that necessary to open the vent valve so that air/vapour can exit through the vent tube 22. Fuel which rises in the by-pass tube 30 may be pushed up to the reservoir 24 but is trapped there and the air/vapour passing through the vent tube 22 bubbles through it and out to the atmosphere via tube 26.

The pressure required to open the vent valve 28 should not be sufficient to create a head of fuel higher than the level of the filler cap 14 above the maximum fuel level because this could cause fuel to be spilled if the cap were removed following expansion of a full tank of fuel.

The location of the by-pass tube 30 remote from the filler pipe ensures that the lower end of the by pass tube is uncovered and the tank vented without a pressure head A when the vehicle is parked on a slope with the filler pipe at the downhill side of the vehicle. The maximum fuel level may then be as shown at B without spillage of fuel.

1. A vehicle fuel tank system comprising: a) a fuel tank (10) having an ullage space (20); b) a filler pipe (12) connected at its lower end to the fuel tank below the ullage space and having a filler cap (14) at its upper end; c) a sensing tube (16) communicating at its lower

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Vehicle fuel tank venting system This invention relates to fuel tank systems for vehicles. Many motor vehicles have a fuel tank with a filler pipe communicating with the fuel tank below an ullage space and a sensing tube connected to the upper end of the filler pipe. The lower end of the sensing tube communicates with the interior of the tank and defines the lower level of the ullage space. When a tank of this kind is filled, air/vapour escapes through the sensing tube until the fuel level reaches the lower end of the sensing tube. The fuel then fills the filler pipe until it reaches the filling nozzle and (assuming the normal kind of nozzle is being used) cuts off further supply of fuel. It is preferable to fit a non-vented filler cap and arrange for venting of the ullage space to allow for withdrawal of fuel from the tank or expansion of fuel into the ullage space. It is a well-known problem with systems of this kind that the ullage space can be "trickle filled" by allowing the level of fuel in the filler pipe to fall as air/vapour exits slowly through the venting system. It is known (see for example German patents 2046562 and 2752645) to close the vent system by a valve actuated by removal of the filler cap or the opening of a flap covering the filler cap. The vent system is thereby closed whenever the fuel tank is being filled so that the ullage space cannot be "trickle filled" but operates normally to vent the tank as soon as the filler cap has been replaced or the flap closed. This arrangement solves the prob lem but is somewhat expensive and can leave the tank unvented if a non-standard filler cap is used or if the flap is accidentally left open. The present invention seeks to prevent "trickle filling" without the use of such a valve. According to the invention we provide a vehicle fuel tank system of the kind described above characterised in that the venting means (21) includes: a valve (28) which can be opened only by a pres sure in the tank (10) sufficient to maintain a head of fuel (A) in the filler pipe (12) and thereby prevent further filling of the tank (10) after the fuel level reaches the lower end of the sensing tube (16). The invention will now be described with refer ence to the accompanying drawings in which: Figure 1 is a sectional view of a vehicle fuel tank system embodying the invention; and Figure 2 is an enlarged view of the circled portion of the fuel tank system of Figure 1. A fuel tank 10 adapted to be mounted at the rear of a motor car (not shown) has a filler pipe 12 con nected at its lower end to the fuel tank 10. A filler cap 14 of the non-venting type is mounted on the upper end of the filler pipe 12. A sensing tube 16 communicates with the upper end of the filler pipe 12 and extends into the fuel tank 10 to define a normal maximum fuel level 18 and an ullage space 20. A venting system 21 includes a vent tube 22 which extends through the highest part of the fuel tank 10 to a reservoir 24. The upper part of reservoir 24 is vented to atmosphere by a downwardly extending tube 26. A check valve 28 in the vent tube 22 below the reservoir 24 comprises a ball 34 cooperating with a seat 32. The weight of the ball 34 is such that it is unseated by a pressure in the tank 10 equivalent to a head of fuel approximately equal to the height of the filler cap 14 above the minimum fuel level 18. A by-pass tube 30 connects the vent tube 22 intermediate the venting valve 28 and the reservoir 24 to the interior of the tank 10 below the maximum fuel level 18 at a location remote from the filler pipe 12. In operation the fuel tank 10 can be filled through the filler pipe 12 until the level of fuel in the fuel tank 10 reaches the lower end of the sensing tube 16. The normal exit of air/vapour from the fuel tank 10 is then cut-off and fuel quickly fills the filler pipe 12 to reach the filler nozzle and shut off the supply of fuel. The lower end of the by-pass tube 30 is below the fuel level. Air/vapour can vent only through the vent valve 28 if the pressure in the tank 10 that which would maintain the head of fuel A in the filler pipe 12. Thus the venting valve 28 prevents venting of the ullage space during filling, thereby preventing overfilling above the maximum fuel level 18. When the filler cap 14 has been replaced, air is drawn into the fuel tank 10 via the by-pass tube 30 as soon as fuel is taken from the fuel tank 10 by the vehicle fuel system (not shown). Expansion of the fuel after filling causes air/vapour pressure to rise above that necessary to open the vent valve so that air/vapour can exit through the vent tube 22. Fuel which rises in the by-pass tube 30 may be pushed up to the reservoir 24 but is trapped there and the air/vapour passing through the vent tube 22 bubbles through it and out to the atmosphere via tube 26. The pressure required to open the vent valve 28 should not be sufficient to create a head of fuel higher than the level of the filler cap 14 above the maximum fuel level because this could cause fuel to be spilled if the cap were removed following expansion of a full tank of fuel. The location of the by-pass tube 30 remote from the filler pipe ensures that the lower end of the by pass tube is uncovered and the tank vented without a pressure head A when the vehicle is parked on a slope with the filler pipe at the downhill side of the vehicle. The maximum fuel level may then be as shown at B without spillage of fuel. CLAIMS

1. A vehicle fuel tank system comprising: a) a fuel tank (10) having an ullage space (20); b) a filler pipe (12) connected at its lower end to the fuel tank below the ullage space and having a filler cap (14) at its upper end; c) a sensing tube (16) communicating at its lower end with the interior of the fuel tank (10) to define the ullage space (20) and at its upper end with the interior of the filler pipe (12) adjacent the filler cap (14), whereby upon filling of the fuel tank (10) air is vented through the sensing tube until the fuel level reaches the lower end of the sensing tube (16), whereupon further fuel fills the filler pipe (12) to prevent filling of the ullage space (20);; d) means venting the ullage space (20) to allow air to enter when fuel is drawn from the fuel tank(1 0) or to allow air/vapour to exit if the fuel in the tank expands into the ullage space (20); characterised by: e) a valve (28) in the venting means (21) which can be opened only by a pressure in the tank (10) sufficient to maintain a head of fuel (A) in the filler pipe (12) and thereby prevent further filling of the tank (10) after the fuel level reaches the lower end of the sensing tube (16).

2. A fuel tank system as claimed in claim 1 characterised in that the venting means includes a by-pass tube (30) connected to the interior of the tank (10) below the ullage space (20) to allow air to enter the tank when fuel is drawn from it.

3. A fuel tank system as claimed in claim 2 characterised in that the by-pass tube (30) is located remote from the filler pipe (12) so that its lower end is uncovered when the vehicle is parked on a slope with the filler pipe directed down the slope to prevent the pressure head (A) created by the venting valve (28) from forcing fuel out of the filler pipe when the cap (14) is removed.

4. A fuel tank system as claimed in any one of the preceding claims characterised by a reservoir (24) in the venting means (21) above the venting valve (28).

5. A vehicle fuel tank system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.