A MOTOR VEHICLE FUEL TANK ARRANGEMENT

Abstract: This invention relates to an anti-trickle filling arrangement for a motor vehicle fuel tank arrangement (11) having a vent passage (22) with a main float valve (32) and a sensing tube (16). The main float valve (32) is surrounded by a tubular wall (34) extending into the tank (12) to a level equal to the normal full level of the tank (12) as determined by the sensing tube (16). When the tank (12) is at the normal full level, the volume within the tubular wall (34) fills with fuel (12) and the main float valve (32) closes the vent passage (22) to prevent trickle filling of the tank (10). When some fuel has been used the fuel level within the tube (34) drops and the main float valve (34) opens. A pressure relief valve (36) opens if the pressure within the thank (10) exceeds a preset value while the main float valve (32) is closed.

Description: A MOTOR VEHICLE FUEL TANK ARRANGEMENT This invention relates to an anti-trickle fill arrangement for a tank, in particular for a motor vehicle fuel tank. Motor vehicle fuel tanks are normally fitted with a vent which allows fuel vapour to escape into the atmosphere, thereby preventing the tank from over pressurizing. Such a vent will usually be fitted with a float valve, also known as a rollover valve, which will automatically close the vent in order to reduce the fuel leakage out of the tank should the vehicle overturn. The vent will usually also be adapted to make it difficult to overfill the tank beyond a normal full level, since overfilling a tank in this way can result in a dangerously small ullage space in the tank. Nevertheless, it can sometimes be possible to overfill the tank by trickle filling it; that is, filling it a very slow rate. It is known from GB 2 269 373A to use a float valve surrounded by a cylindrical skirt having a small orifice towards its upper end to make it more difficult to overfill the tank. According to the invention, there is provided a motor vehicle fuel tank arrangement comprising: a fuel tank; a vent passage for communicating the fuel tank to the atmosphere; a float valve for controlling flow through the vent passage; and a skirt surrounding the float valve, the skirt extending at least in part in a generally downward direction into the fuel tank, the motor vehicle fuel tank arrangement being characterized in that it further comprises a pressure relief valve which opens if the pressure within the fuel tank exceeds a pre-set value. Although the invention has a wider application, for convenience the invention will henceforth be described with reference to fuel in the liquid state and fuel vapour . Preferably, the tank will further comprise a sensing tube having one end that extends into the fuel tank in a generally downward direction and another end that communicates with the atmosphere when the tank is being filled. As the tank is initially being filled, the fuel level in the tank will rise and in so doing will expel fuel vapour from the ullage space in the tank through the sensing tube and through the vent passage. When the fuel level reaches the bottom of the sensing tube, vapour can no longer flow out of the ullage space through the sensing tube, and the vapour will then be expelled though the vent passage only, usually at a lower rate since the vent passage is normally narrower than the sensing tube . When the fuel level reaches the bottom end of the skirt, vapour from the ullage space will no longer be able to escape through the vent passage, and the fuel level in the main area of the tank will cease to rise. However, because the float valve is normally in the open position, the volume within the skirt remains in communication with the vent passage and the fuel level within the skirt can continue to rise, until it rises sufficiently so as to close the float valve. When the float valve is closed, no further filling of the tank can take place. The float valve will preferably be placed towards the top of the skirt, but it may alternatively be placed towards the lower end of the skirt . The fuel level in the skirt will only drop when fuel is consumed by the vehicle engine because fuel can only escape under the skirt. Until this occurs, the float valve remains closed, and so the tank cannot easily be over filled by trickle filling fuel into it at a slow enough rate. The use of a pressure relief valve reduces the risk that the tank will over pressurize while the float valve is closed. When the pressure within the tank exceeds the pre-set value, the pressure relief valve will open and release the excess pressure. The pre-set value may be chosen in accordance with the maximum safe pressure in the tank, but preferably, the pre set pressure value at which the pressure relief valve opens is substantially equal to the pressure due to the head of liquid in the tank filler pipe when the filler pipe is full. Thus the pressure relief valve remains closed if the tank is filled and the fuel level rises up the tank filler pipe, but excess pressure due to the subsequent evaporation of fuel (after the tank has been sealed by a filler cap) can be released through the pressure relief valve. The bottom of the skirt may extend to a level that is slightly higher than the bottom of the sensing tube. However, the bottom of the skirt will preferably extend to a level that is substantially coincident with the bottom of the sensing tube, so that the normal full level is determined by the level of the bottom of the sensing tube. Here, the term normal full level will be understood to mean the level to which the tank is designed to be filled. To reduce the amount of fuel consumption it takes for the valve to open after the tank has been normally filled, the skirt will preferably closely surround the float valve. For simplicity, the skirt may be a tube. The tube will preferably have a circular cross section, and will preferably be substantially cylindrical. A second float valve controlling communication between the tank and the pressure relief valve will preferably be provided, to reduce the risk of fuel entering the vent passage. The vent passage float valve and the pressure relief float valve will preferably be spaced apart to make it less likely that both float valves would be submerged when a vehicle with the fuel tank arrangement is positioned on an inclined surface. The vent passage may lead directly to the atmosphere, but will preferably lead first to a vapour recovery arrangement to reduce the amount of fuel vapour being released. The invention will now be further described, by way of example, with reference to the accompanying drawings in which: Figure 1 shows a cross sectional schematic view of a fuel tank according to the invention, with the fuel at its normal full level; and Figure 2 shows a view corresponding to Figure 1 but where some fuel as be used. A vehicle fuel tank arrangement 11 is shown in Figure 1 having a fuel tank 10 containing liquid fuel 12 at the normal full level 14, before any fuel has been consumed. The normal full level in the main area of the tank 10 is determined by the level of the bottom end of a sensing tube 16 descending into the tank 10. The top end of the sensing tube 16 is in communication with the tank filler pipe 18, so as fuel 12 initially enters the tank 10 through a filler nozzle 20 inserted into the filler pipe 18 , fuel vapour can be expelled from the tank 10 through the sensing tube 16 and into the atmosphere through the open filler pipe 18. However, when the fuel 12 in the tank 10 reaches the bottom of the sensing tube 16, fuel vapour can no longer escape through the sensing tube 16. The filler pipe 18 enters the tank at a level that is bellow the bottom of the sensing tube 16, so vapour is prevented from escaping through the filler pipe 18 when the fuel 12 in the tank 10 reaches the bottom of the sensing tube 16. Under normal conditions, the tank 10 is vented by a vent passage 22 which leads to a fuel vapour recovery arrangement 38 and ultimately to the atmosphere. The vent passage 22 allows evaporating fuel to leave the tank and reduces the risk that the tank 10 will over pressurize. Communication with the vent passage 22 is governed by a main float valve 32 mounted on an upper region of the tank 10. A continuous tubular wall 34 surrounds the main float valve 32 and extends from the tank wall in a downward direction to a level 17 that is substantially equal to the level 15 of the bottom of the sensing tube 15. Hence when the fuel 12 in the tank 10 has reached the bottom of the sensing tube 16, the tubular wall 34 prevents fuel vapour being expelled from the main part of the tank through the vent passage 22 and only vapour contained within the tubular wall 34 can escape. Since the fuel vapour in the main part of the tank cannot escape through the sensing tube 16, any further rise in the fuel level 14 in the main part of the tank 10 is prevented so that an ullage space 30 remains above the fuel level 14. Although vapour within the ullage space 30 is trapped when the fuel level 14 reaches the bottom of the sensing tube 15, vapour within the tubular wall 34 can still escape through the vent passage 22 since the main float valve 32 will be open. Hence any further intake of fuel will result in the fuel level within the tubular wall 34 rising, until this fuel level is high enough to lift the main float valve 32 to close access to the vent passage 22. This is the situation shown in Figure 1. Any attempt to further fill the tank will only result in an overflow through the filler pipe 18, making it impossible to completely fill the tank 10 by trickle filling it. It will be understood that if the bottom end 17 of the tubular wall 34 were to extend to a level that is above the end of the sensing tube 15, then the fuel level 14 in the main part of the tank 10 would be able to rise past the end 15 of the sensing tube 16 and the normal full level would be determined by the position of the bottom end 17 of the tubular wall 34. After some fuel has been consumed by the vehicle engine, as shown in Figure 2, the fuel level in the tubular wall will fall, thereby opening the main float valve 32 so that the tank is open to the vent passage 22 and the atmosphere. Although the ullage space 30 will not be in communication with the vent passage 22 until the fuel level drops to a level below the bottom end 17 of the tubular wall 34, the ullage space will be free to expand by forcing the level of fuel in the tubular 34 wall to rise (until the float valve 34 closes again) . To reduce the amount of fuel that needs to be consumed before the main float valve 32 opens, the tubular wall 34 closely surrounds the main float valve 32. To reduce the risk of the tank 10 pressurizing when the filler pipe is sealed by a filler cap (not shown) and before the fuel level has dropped to open the main float valve 32, a pressure relief valve 36 connects the tank 10 to the vent passage 22. The pressure relief valve 36 is normally closed but is set to open when the pressure inside the tank 10 exceeds atmospheric pressure by a predetermined amount. The pressure needed to open the relief valve 36 is set to be just above the pressure in the tank when the filler pipe 18 is full of fuel, so that the pressure relief valve 36 remains closed as the tank is being filled. However, the pressure relief valve 36 can open if the pressure in the tank rises due to the evaporation of fuel, after the filler cap has been replaced. Although the filler cap may have a pressure relief bypass valve, this valve will be set to open at a pressure set in a accordance with the maximum safe pressure of the tank. The pressure relief 36 valve in the vent passage 22 is set to open at a lower pressure than the maximum safe pressure, thereby helping to lower the maximum pressure possible in the tank after the tank has been filled. A subsidiary float valve 40 is provided between the tank and the pressure relief valve 36 to reduce the risk of fuel entering the vent passage 22. Although the pressure relief valve 36 is shown connected to the same vent passage 22 as the main float valve 40, the pressure relief valve could instead be connected to a separate vent passage . Once sufficient fuel has been used for the fuel level to fall below the bottom end 17 of the skirt, the ullage space 30 will be in communication with the vent passage 22 and the tank 10 will be vented in the normal way, and will therefore be at a pressure close to atmospheric pressure. Hence it is unlikely that an unpleasant and/or dangerous puff of fuel vapour will be released from tank 10 when the filler cap is removed, since the filler cap is only normally removed to refill the tank. From this description, it will be appreciated that the invention provides several safety improvements in the design of motor vehicle fuel tanks.

Claims: Claims : 1. A motor vehicle fuel tank arrangement (11) comprising: a fuel tank (10) ; a vent passage (22) for communicating the fuel tank (10) to the atmosphere; a float valve (32) for controlling flow through the vent passage (22) ,- and a skirt (34) surrounding the float valve (32) , the skirt (34) extending at least in part in a generally downward direction into the fuel tank (10) , the motor vehicle fuel tank arrangement being characterized in that it further comprises a pressure relief valve (36) which opens if the pressure within the fuel tank (10) exceeds a pre-set value . 2. A motor vehicle fuel tank arrangement (11) as claimed in Claim 1 wherein the motor vehicle fuel tank arrangement (11) further comprise a sensing tube (16) one end of which extends into the fuel tank (10) in a generally downward direction and the another end of which communicates with the atmosphere. 3. A motor vehicle fuel tank arrangement (11) as claimed in any previous claim wherein the bottom end (17) of the skirt (34) extends to a level that substantially equal to the bottom end (15) of the sensing tube (16) . 4. A motor vehicle fuel tank arrangement (11) as claimed in any previous claim wherein the skirt (34) closely surround the float valve (32) . 5. A motor vehicle fuel tank arrangement (11) as claimed in any previous claim wherein the skirt (34) has the form of a tube . 6. A motor vehicle fuel tank arrangement (11) as claimed in Claim 6 wherein the tube (34) is substantially cylindrical . 7. A motor vehicle fuel tank arrangement (11) as claimed in any previous claim wherein a second float valve (40) controlling communication between the fuel tank (10) and the pressure relief valve (36) is provided. 8. A motor vehicle fuel tank arrangement (11) as claimed in Claim 7 wherein the second float valve (40) is spaced apart from the main float valve (32) . 9. A motor vehicle fuel tank arrangement (11) as claimed in any previous claim wherein the vent passage (22) leads to a vapour recovery arrangement (38) . 10. A motor vehicle as claimed in any previous claim wherein the fuel tank arrangement (11) comprises a filler pipe (18) , and the pre set pressure value at which the pressure relief valve opens is substantially equal to the pressure due to the head of liquid in the filler pipe (18) when the filler pipe (18) is full.

Inventors: BOWLES DAVID THOMAS, FITZGERALD ANTHONY ALAN, BOWLES, DAVID, THOMAS, FITZGERALD, ANTHONY, ALAN
Applicants: BOWLES DAVID THOMAS, FITZGERALD ANTHONY ALAN, FORD GLOBAL TECH INC, BOWLES, DAVID, THOMAS, FITZGERALD, ANTHONY, ALAN, FORD GLOBAL TECHNOLOGIES, INC.
Application year: 2000
Main classification: B60K15
IPC codes: B60K15