GB2272894A

GB2272894A - An anti-trickle filling arrangement for a fuel tank

Info

Publication number: GB2272894A
Application number: GB9224815A
Authority: GB
Inventors: Michael C Rogers
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1992-11-26
Filing date: 1992-11-26
Publication date: 1994-06-01
Also published as: GB9224815D0

Abstract

An anti-trickle filling arrangement for a fuel tank 12 which has a vent line 32 leading to a vapour recovery canister 34 and a vent to atmosphere valve 36 downstream of the canister uses a sensor to detect when re-fuelling is taking place. When re-fuelling is detected, the valve 36 is closed to shut off the fuel tank vent to atmosphere and thus to prevent trickle filling. The sensor may be a "cap off" sensor 22 or may be a fuel level sensor (122, Figure 2), the rate of fuel level change being monitored and when the rate exceeds a certain level a signal causing processor 14 to shut off valve 36. The valve is reopened either by a "cap-on condition being sensed by sensor 22 or upon restarting the engine or after a time delay. A sensing tube 24 is also provided which allows air and/or free vapour to be expelled during refuelling. <IMAGE>

Description

AN ANTI-TRICKLE FILLING ARRANGEMENT FOR A FUEL TANK This invention relates to an anti-trickle filling arrangement for a motor vehicle fuel tank.

Motor vehicle fuel tanks are intended to be filled with fuel to a level which leaves an ullage space at the top of the tank. This ullage space is normally filled with fuel vapour, and the space is required to accommodate fuel/vapour expansion under varying climatic conditions.

However in order to prevent the internal pressure in the fuel tank from rising too high, it is conventional to provide a vent from the tank through which fuel vapour (but not liquid) can escape. In the past this vapour has been allowed to escape to atmosphere, but with the arrival of ever stricter emission controls, it is now required that the fuel be extracted from the vapour/gas mixture flowing along the vent pipe before the remaining, fuel-free, gases are discharged to atmosphere.

The maximum level to which the tank can be filled is normally determined by a sensing tube through which air or gas is discharged from the tank during filling. As soon as the lower end of the sensing tube is immersed in liquid fuel, then no more gas can escape and the fuel level rises rapidly in the filler pipe to prevent further filling.

However whilst the vent from the top of the tank remains open, it is still possible to charge fuel into the tank, albeit at a very low rate commensurate with the rate at which vapour can pass through the vent line. This practice, referred to as trickle filling, is very much to be discouraged because if the ullage space of the tank is filled with liquid fuel the desired protection against fuel expansion is not achieved and under extreme conditions the tank could rupture.

It is known to include a dedicated valve in the vent line which closes the vent line during re-fuelling and opens the vent line once re-fuelling is completed. In a known system, the valve is opened or closed in response to the pressure signalled within the filler neck, close to the position of the filler cap. During normal running of the vehicle with the filler cap in place the pressure sensed by this valve will be superatmospheric. However as soon as the cap is removed for re-fuelling, the pressure will fall to atmospheric pressure and this pressure change can be used to open or close the anti-trickle valve.

The use of such a valve however requires a dedicated valve and a dedicated signal line leading to the valve.

According to the present invention, there is provided an anti-trickle filling arrangement for preventing overfilling of a fuel tank associated with an onboard vapour recovery system which system includes a valved vent to atmosphere downstream of an onboard vapour recovery unit, the arrangement including a sensor which produces a signal to indicate that re-fuelling is taking place, and means for closing the valved vent in response to such a signal.

By using the valved vent of the onboard vapour recovery system to also prevent anti-trickle filling, it is possible to dispense with one valve and its associated signal line.

This saves both cost and packaging space.

The sensor may be a "cap-off" sensor which provides an electrical signal when the cap is off to close the valved vent.

In an alternative, the sensor may be the tank sender unit which monitors the fuel level in the tank at all times. The rate of fuel level increase can be monitored by the tank sender unit, and an onboard processor can receive the signal from the sender unit and process this signal to decide whether it indicates the rate of increase corresponds to tank refilling.

When a "cap-off" sensor is used, the valved vent will be reopened when the "cap-on" condition is sensed. When the tank sender unit is used as the sensor, the valved vent will be re-opened either upon re-starting the engine of the vehicle, or after a time delay of five minutes, whichever is the shorter.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram illustrating a first anti-trickle filling arrangement in accordance with the invention; and Figure 2 is a schematic diagram of a second embodiment of the invention.

The arrangement shown in Figure 1 includes an engine 10 and a fuel tank 12. A processor 14 is connected to the engine and performs various engine management functions in a manner which is itself well known.

The fuel tank 12 has a filler neck 18 and a filler cap 20.

In Figure 1 the cap 20 is shown removed from the filler neck to allow re-fuelling. A sensor 22 is fitted adjacent to the filler neck 18 to detect the presence or absence of the cap 20. The filler cap 20 may for example include a magnet, the presence or absence of which is sensed by a Hall effect sensor or by a variable reluctance sensor 22. However other methods of sensing the presence or absence of the cap 20 can also be used.

As the tank 12 is filled with fuel, air and/or fuel vapour is expelled through the filler neck 18 and/or through a sensing tube 24.

The tank 12 is fitted with two vent openings 26, 28 which are connected through a T-piece 30 into a common vent line 32. The vent line 32 passes through a carbon canister 34 where fuel vapour is extracted from the gas stream, and the clean gas stream is then vented to atmosphere through a vent valve 36.

At the time of re-fuelling, the cap 20 is removed from the filler neck 18. This is sensed by the sensor 22 and a signal is sent through a signal line 38 to the processor 14.

The processor 14 then passes a signal along a line 40 to the vent valve 36 to close this valve. Closing the valve 36 prevents any flow through the vent line 32 and therefore effectively closes the vents 26, 28. Whilst the cap 20 is off therefore there can be no flow through the vent line 32 and therefore as soon as the lower ends of the filler neck 18 and of the sensing tube are immersed by the rising liquid fuel level, any further fuel charged to the tank will merely cause the level in the filler neck 18 to rise.

When re-fuelling is completed and the cap 20 is replaced, this replacement will be sensed by the sensor 22 and a signal will be given by the processor 14 to the valve 36 so that this valve opens. The vent passage necessary for proper venting of the tank 12 is then open and ready for use.

The arrangement shown in Figure 2 is substantially similar to that shown in Figure 1 and corresponding components carry the same reference numerals. However in place of the "capoff" sensor 22, a liquid fuel level sensor 122 is provided in the tank, and this is connected by a signal line 138 to the processor 14. The sensor 122 can be the conventional fuel level sensor which continuously monitors the fuel level for the information of the driver. When the rate of fuel level increase as sensed by the sensor 122 exceeds a pre-set level, then the processor 14 switches the valve 36 to the closed position to prevent venting through the vent line 32.

The rate of increase which triggers the closing of the valve 36 needs to be above a pre-set level to avoid closure of the valve following on small increases in fuel level due to thermal expansion, where closure of the vent will be highly undesirable.

The processor 14 can provide a signal to open the valve 36 either when the engine 10 is re-started, or five minutes after closure, whichever is the shorter time interval.

It is an advantage of the embodiment shown in Figure 2 that no additional sensors are required; the sender unit 122 is already present in each fuel tank, and it is only necessary to provide the necessary processing capability to deduce, from the rate of level change, when re-fuelling is taking place.

The valve 36 is also present in any case. Apart from the anti-trickle fill function just described, that valve is present to allow leak testing of the system. In a fuel system with onboard vapour recovery, it is necessary to regularly close the system for a short time (by closing the valve 36) and then to monitor the rate of pressure change within the system. This is done to indicate whether or not the system has any leaks. The present invention therefore makes use of a valve which is already present in the system, rather than providing a specific, dedicated valve for the purposes of preventing trickle filling.

Claims

1. An anti-trickle filling arrangement for preventing overfilling of a fuel tank associated with an onboard vapour recovery system which system includes a valved vent to atmosphere downstream of an onboard vapour recovery unit, the arrangement including a sensor which produces a signal to indicate that re-fuelling is taking place, and means for closing the valved vent in response to such a signal.

2. An anti-trickle filling arrangement as claimed in Claim 1, wherein the sensor is a "cap-off" sensor which provides an electrical signal when the fuel tank filler cap is off to close the valved vent.

3. An anti-trickle filling arrangement as claimed in Claim 1, wherein the sensor is a tank sender unit which monitors the fuel level in the tank at all times, and wherein the rate of fuel level increase is monitored by the tank sender unit, and signalled to an onboard processor which processes this signal to decide whether it indicates a rate of increase corresponding to tank refilling.

4. An anti-trickle filling arrangement as claimed in Claim 2, wherein the valved vent will be re-opened when the "capon" condition is sensed.

5. An anti-trickle filling arrangement as claimed in claim 3, wherein the valved vent will be re-opened either upon restarting the engine of the vehicle, or after a time delay of five minutes, whichever is the shorter.

6. An anti-trickle filling arrangement substantially as herein described with reference to one of the embodiments shown in the accompanying drawings