GB2283233A

GB2283233A - Checking tightness of fuel tank venting system;correct sealing of filler cap

Info

Publication number: GB2283233A
Application number: GB9322455A
Authority: GB
Inventors: Ronald Peter Pardy
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1993-10-30
Filing date: 1993-10-30
Publication date: 1995-05-03
Also published as: GB9322455D0

Abstract

A fuel tank pressure sensing arrangement used to monitor the tightness of a fuel tank venting system comprises a fuel tank 1 with a filler tube 2 in direct communication with an air space above fuel in the tank 1 and closable by a filler cap 3, the filler cap 3 incorporating a pressure sensor 19 sensitive to pressure changes within the filler tube 2 when the filler cap 3 is in a proper closing position on the filler tube 2. The sensor 19 is capable of producing an electrical signal enabling such pressure changes to be monitored and electrical connections enabling such monitoring are made between the sensor 19 and monitoring circuitry by two electrical contacts on the cap making contact with two contacts (15, Figure 3) on the outer surface of the filler tube when the cap is properly closed. The sensor 19 and the monitoring circuitry include means to indicate that the said electrical connections have been made only when the filler cap 3 is in its proper closing position on the filler tube 2. The cap may incorporate a pressure relief valve 22 with which the sensor is integrated. The electrical contacts on the filler tube may be connected to the monitoring circuitry via a safety switch, eg the ignition switch of the vehicle. The cap may screw into the filler tube. <IMAGE>

Description

FUEL TANK PRESSURE-SENSING ARRANGEMENT This invention relates to a fuel tank pressure-sensing arrangement, particularly, but not exclusively, for the fuel tank of a motor vehicle.

As is well known, with an increasing awareness of the effects of environmental pollution on health, attention has been directed to developing means whereby pollution may be reduced. One area of particular concern has been the pollution arising from the release of hydrocarbon and other fuel vapours into the atmosphere.

In this connection, the motor industry has developed, socalled, on-board diagnostics to enable the integrity of the fuel system of a motor vehicle to be tested prior to the commencement of each journey undertaken. To this end, provisions have been made on commercial vehicles for the fuel tank and associated venting ducts and vapour filter devices to be subjected to an elevated or reduced pressure, the level of which is then monitored over a set period of time to check whether it is held or changes significantly.

Depending on the degree of any change, it is assessed as indicating either a significant leak in the system or an acceptable pressure variation.

Customarily, in such a test, fuel systems of motor vehicles are subjected to a reduced pressure by way of a vacuum duct connectable to the induction manifold of the engine of the motor vehicle by a valve, often referred to as a purge valve. Conveniently, such a purge valve is arranged to be a solenoid operated valve. A breather tube for the fuel tank and normally arranged to vent the air space above the fuel in the tank to the free atmosphere via an absorption canister to remove fuel vapour, is closed by a valve during the test procedure. During the test procedure, the pressure in the air space above the fuel in the tank is customarily monitored by means of a pressure sensor or pressure gauge installed in the top of the tank.

With such an arrangement, the procedure followed for the purpose of testing the fuel system, is for the valve on the out-let end of the breather tube to be closed and for the purge valve to be opened. With the engine running, the reduced pressure in the induction manifold is transmitted to the air-space in the tank and to the associated venting ducts and filter device attached thereto by opening the purge valve. The pressure sensor monitors the fall in pressure until a prescribed level is reached. At this point the purge valve is closed. Conveniently, the sensor incorporates a transducer which produces a signal which is used by electrical circuitry to cause the solenoid purge valve to close automatically when the prescribed pressure level is reached. The sensor continues to monitor the reduced pressure in the air space over a pre-set time, as described above, to enable any leak in the system to be detected and assessed. Via appropriate circuitry, an alarm signal, which may be audible or visual, may be produced in the event of a significant leak in the system being diagnosed.

Such known arrangements can give rise to misleading test results due to the fuel cap having been left off the tank filler tube or not having been properly replaced to adequately seal the fuel tank filler tube.

According to the present invention, there is provided a fuel tank pressure-sensing arrangement comprising a fuel tank having a filler tube attached thereto, said filler tube being in direct communication with an air space above fuel in the tank and closable by a filler cap, wherein the filler cap incorporates a pressure sensor sensitive to pressure changes within the filler tube when the filler cap is in a closing position on the filler tube, said sensor being capable of producing an electrical signal enabling such pressure changes to be electrically monitored and wherein electrical connections enabling such electrical monitoring are made between the pressure sensor and monitoring circuitry only by the cap being in its proper closing position on the filler tube, and wherein the sensor and the monitoring circuitry include means to indicate that the said electrical connections have been made only when the filler cap is in its proper closing position on the filler tube.

By means of this invention, the above-mentioned problem of misleading test results arising from a fuel tank filler cap not being properly in place, may be avoided since the absence of the electrical connections being made between the pressure sensor and the monitoring circuitry can be immediately observed by the test operator, normally the vehicle driver. Because of the rapid fault diagnosis that this invention provides, test cycle times can be reduced, saving both man-power and fuel. Further, since the electrical connections for the pressure sensor can also be used in establishing that the filler cap is in its proper closing position on the fuel tank filler tube, the cost of electrical installation may be kept low. Still further, because, in the present invention, the pressure sensor is incorporated in the fuel tank filler cap, it is readily fitted to the filler tube of the fuel tank and is easily accessible for servicing or replacement, whereby fitting and servicing costs may be kept low.

The fuel tank in the fuel tank pressure sensing arrangement of the present invention may be any fuel tank which may be subjected to an elevated or reduced pressure. However, while it may therefore be a tank for heating-fuel, for example, it is preferably a motor vehicle fuel tank.

The filler tube attached to the fuel tank should be such as to be closable by a filler cap, substantially in sealing manner as will be described further below. The filler tube should also be such that electrical connections can be made, between the pressure sensor incorporated in the filler cap and the monitoring circuitry, only by the cap being in its proper closing position on the filler tube. To this end, the filler tube is preferably provided with two electrical contacts on its outer surface adjacent the end being closed by the cap. While one of these may be a direct electrical contact with the tube itself, it is preferred that both contacts are electrically isolated from the tube. The contacts are preferably circumferentially spaced from one another.

The filler cap in the fuel tank pressure sensing arrangement of the present invention should incorporate a pressure sensor sensitive to pressure changes within the filler tube when the cap is in a closing position on the filler tube, the sensor being capable of producing an electrical signal enabling such pressure changes to be monitored. The pressure sensor is preferably incorporated in the cap so that it is located within the filler tube when the cap is in a closing position on the filler tube. The pressure sensor may be a pressure transducer capable of producing an electrical signal which varies continuously over the range of pressures of interest, as by way of an integral potentiometer, for example, or alternatively, capable of producing an electrical signal at specific pressures as by the making of integral switches, for example.

The filler cap should be such that electrical connections can be made between the pressure sensor and the monitoring circuitry only by the cap being in its proper closing position on the filler tube. To this end it is preferred that the filler cap is provided with two electrical contacts to which the pressure sensor is electrically connected.

These contacts are preferably positioned so that they are situated externally of the filler tube and make electrical connections with cooperating contacts on the outer surface of the filler tube wall, when the filler cap is in a closing position on the filler tube. It is preferred that both contacts are electrically isolated from the filler cap body which houses the pressure sensor. Preferably the contacts are circumferentially spaced from one another on the filler cap.

It will be appreciated that the filler cap should be such as to ensure pressure communication between the atmosphere within the filler tube and the pressure sensor. In that connection, it is preferred that the sensor is in direct communication with the atmosphere within the filler tube when the filler cap is in a closing position on the filler tube.

The filler cap preferably incorporates a pressure relief valve whereby the build up of any undesirably high pressure within the filler tube, such as might tend to arise from a motor vehicle being exposed to excessive heat from the sun, for example, can be avoided. It is especially preferred that the pressure sensor is integrated with such a pressure relief valve. To this end, it is preferred that the pressure sensor is positioned in the filler cap such as to be in direct communication with the atmosphere in the filler tube on one side and in direct communication with the free atmosphere on an opposite side. In particular, it is preferred that the pressure sensor has the added function of acting as a pressure relief valve in the above context.

The filler cap may be fitted with a gasket to ensure proper closing of the filler tube. The filler cap may be provided with any securing means whereby it can be located and secured in a closing position on the filler tube. It is preferred that it is provided with a screw thread to cooperate with a screw thread on the internal wall of the filler tube.

The monitoring circuitry in the fuel tank pressure sensing arrangement of the present invention is preferably electrically connected to electrical contacts on the filler tube. Such connection is preferably via a safety switch, such as the ignition switch of a motor vehicle in which the pressure sensing arrangement may be installed. Preferably, such a safety switch can be used to electrically isolate the pressure sensor and intermediate electrical contacts from energization. The monitoring circuitry may include any means by which signals produced by the pressure sensor can be monitored. Such means may include digital or analog displays, warning lights and buzzers, for example.

The sensor and the monitoring circuitry should include means to indicate that the electrical connections are made between them when the filler cap is in its proper position on the filler tube. To this end, it is preferred that the sensor is such that it is capable of completing the monitoring circuitry at atmospheric pressure so that when the monitoring circuitry is energised it can monitor its connection to the sensor. Indication of such connection may be a reading on a pressure monitor or the illumination of a lamp in the monitoring circuitry.

It is preferred, however, that the monitoring circuitry is such that, when energised after electrical connection to the pressure sensor by the filler cap being in a closing position on the filler tube, it activates a relay switch to prevent a warning light being lit which would otherwise indicate disconnection of the sensor and therefore that the filler cap was not in a closing position on the filler tube.

Clearly, absence of any response from the sensor could equally indicate the same fault, but it is preferred that the monitoring circuitry includes a light or audible signal to indicate the condition of the circuit.

It is preferred that the sensor and the monitoring circuitry are such that they are able to cooperate in the control of a solenoid operated valve in response to a prescribed pressure level being sensed, and other such devices.

In the latter connection it is preferred that the monitoring circuitry incorporates a timing means and means to produce a visual or audible warning if an undesirable pressure change is monitored by the monitoring circuitry over a preset period.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a sketch illustrating a motor vehicle fuel tank and an associated venting system, which tank is employed in a fuel tank pressure sensing arrangement according to the present invention.

Figure 2 is a sketch illustrating in detail the fuel tank filler cap employed in a closing position on the filler tube of the fuel tank shown in Figure 1.

Figure 3 is a sketch of an end view of the filler tube shown in Figures 1 and 2.

In the drawings in which like numbers are used to indicate like parts; Figure 1 shows the fuel tank 1 to which is attached a fuel filler tube 2 closable by the filler cap 3.

Connected to the tank 1 is a tank venting system comprising the venting valves 4, the venting duct 5, the vapour absorption canister 6 having a breather tube 7 closable by a valve 8. The absorption canister 6, which contains activated carbon ( not shown ), is connectable to the induction manifold 9 of the motor vehicle engine 10 via the purge duct 11 and the solenoid operated purge valve 12. The air space above the fuel in the fuel tank 1 communicates with the inside of the upper part of the filler tube 2 by means of the breather duct 13. The wire conductors 14 which are electrically attached to the two electrical contacts 15 ( Figure 3 ) on the outer surface of the filler tube, have their other ends connected into a circuit ( not shown ), for monitoring electrical signals produced by the pressure sensor and for monitoring its own electrical connection to the sensor.

Figure 2 shows details of the filler cap 3 which has a screw threaded body 16 cooperating with the screw threads 17, formed on the inner wall of filler tube 2, to close the filler tube 2 by bringing the gasket 18 in firm, sealing engagement with the end of the filler tube 2. Within the threaded body 16 of the filler cap 3 is positioned the pressure sensor 19. The pressure sensor 19 is of the type having an integral potentiometer and thereby providing a signal proportional to the pressure sensed. The pressure sensor 19 is electrically connected to two electrical contacts isolated from the filler cap and positioned to be circumferentially spaced on the under side of the top of the cap so as to make electrical connection with contacts 15 on the outside wall of the filler tube 2 with the cap in its closing position.

The pressure sensor 19 is in communication with the pressure within the filler tube 2 via the aperture 20 in the threaded body 16 of the cap 3. Through the top of the cap 3 is a pressure vent 21 which communicates with an air space 22 above the sensor 19 which is resiliently mounted in the cap 3 in such a manner that it can act as a pressure relief valve, as an added function, to prevent undesirable pressure build-up in the filler tube The monitoring circuitry ( not shown ), connected to the wire conductors 14 includes an electrical relay switch which, when activated by the monitoring circuitry being energised with the sensor 19 completing the circuit, interrupts an auxiliary circuit of the monitoring circuitry to prevent a warning light being illuminated and which would otherwise indicate failure of the connection of the monitoring circuitry to the sensor 19 and that the filler cap 3 was not in a closing position on the filler tube 2.

The monitoring circuitry also includes an analog meter to monitor the electrical signals produced by the pressure sensor 19. Also included is a relay switch which is automatically activated, when the pressure sensed by the sensor 19 is a preset minimum, to cause, via an auxiliary circuit, the solenoid purge valve 12 to be closed. Further included in the monitoring circuitry, is a timer and an audible warning device which is automatically activated if an undesirable pressure change is detected within a pre-set period.

In operation of the pressure sensing arrangement illustrated; the fuel tank 1 containing fuel ( not shown has its filler tube 2 closed by the filler cap 3 which brings two electrical contacts on the cap into contact with the contacts 15 on the filler tube to electrically connect the monitoring circuitry to the pressure sensor 19. The monitoring circuitry is then energised by switching on the ignition switch of the engine 10. Energising the monitoring circuitry, made possible by the circuit being completed by the sensor 19, causes the relay switch ( not shown ) to be activated whereby no warning lamp is illuminated. The engine 10 is started which gives rise to a reduced pressure in the manifold 9. The valve 8 on the breather tube 7 is then closed and solenoid operated purge valve 12 is opened.

The reduced pressure thus applied to the fuel tank 1 and thereby to the filler tube 2 is sensed by the pressure sensor 19 which produces a signal proportionate thereto.

When the preset minimum pressure is reached, the appropriate relay switch in the monitoring circuitry is automatically activated to cause the solenoid purge valve 12 to close.

The pressure in the filler tube 2 is then monitored over a pre-set time to determine whether any significant leak exists in the fuel tank and associated venting system, the audible warning device being activated if affirmative.

Thereafter, the valve 8 is reopened to return the fuel tank 1 to being vented via the absorption canister 6. In the event that, for any reason, there is a tendency for pressure in the filler tube 2 to increase towards an undesirably high level, the resilient mounting of the sensor 19 in the cap body 16 will permit the sensor 19 to be lifted from its seating over the aperture 20 and allow excess pressure to escape past the sensor 19 to the free atmosphere through the pressure vent 21.

Claims

1. A fuel tank pressure-sensing arrangement comprising a fuel tank having a filler tube attached thereto, said filler tube being in direct communication with an air space above fuel in the tank and closable by a filler cap, wherein the filler cap incorporates a pressure sensor sensitive to pressure changes within the filler tube when the filler cap is in a closing position on the filler tube, said sensor being capable of producing an electrical signal enabling such pressure changes to be electrically monitored and wherein electrical connections enabling such electrical monitoring are made between the pressure sensor and monitoring circuitry only by the cap being in its proper closing position on the filler tube, and wherein the sensor and the monitoring circuitry include means to indicate that the said electrical connections have been made only when the filler cap is in its proper closing position on the filler tube.

2. A fuel tank pressure-sensing arrangement as claimed in Claim 1 wherein the fuel tank is a motor vehicle fuel tank.

3. A fuel tank pressure-sensing arrangement as claimed in either of Claim 1 or Claim 2 wherein the filler tube is provided with two electrical contacts on its outer surface adjacent the end being closed by the cap.

4. A fuel tank pressure-sensing arrangement as claimed in Claim 3 wherein the electrical contacts on the outer surface of the filler tube are electrically isolated from the tube and are circumferentially spaced from one another.

5. A fuel tank pressure-sensing arrangement as claimed in any one of the preceding claims wherein the pressure sensor is located within the filler tube when the cap is in a closing position on the filler tube.

6. A fuel tank pressure-sensing arrangement as claimed in any one of Claims 3, 4, or 5 wherein the filler cap is provided with two electrical contacts to which the pressure sensor is electrically connected positioned to make electrical connections with the contacts on the outer surface of the filler tube.

7. A fuel tank pressure-sensing arrangement as claimed in any one of the preceding claims wherein the filler cap incorporates a pressure relief valve with which the pressure sensor is integrated.

8. A fuel tank pressure-sensing arrangement as claimed in Claim 7 wherein the pressure sensor has the added function of acting as the pressure relief valve.

9. A fuel tank pressure-sensing arrangement as claimed in any one of the preceding claims wherein the monitoring circuitry is electrically connected to electrical contacts on the filler tube via a safety switch.

10. A fuel tank pressure-sensing arrangement as claimed in Claim 9 wherein the safety switch is the ignition switch of a motor vehicle.

11. A fuel tank pressure-sensing arrangement as claimed in any one of the preceding claims wherein the pressure sensor is such that it is capable of completing the monitoring circuitry at atmospheric pressure.

12. A fuel tank pressure-sensing arrangement as claimed in any one of the preceding claims wherein the monitoring circuitry is such that when energised after electrical connection to the pressure sensor it activates a relay switch to prevent a warning light being lit.

13. A fuel tank pressure-sensing arrangement as claimed in any one of the preceding claims wherein the monitoring circuitry and the sensor are such that they can cooperate in the control of a solenoid operated valve.

14. A fuel tank pressure-sensing arrangement as claimed in any one of the preceding claims wherein the monitoring circuitry includes a timing means and means to produce a visual or audible warning if an undesirable pressure change is monitored by the monitoring circuitry within a preset period.

15. A fuel tank pressure-sensing arrangement as claimed in any one of the preceding claims substantially as described herein with reference to the accompanying drawings.