GB2254847A

GB2254847A - Fuel tank

Info

Publication number: GB2254847A
Application number: GB9108456A
Authority: GB
Inventors: Ronald Pardy
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1991-04-19
Filing date: 1991-04-19
Publication date: 1992-10-21
Also published as: GB9108456D0

Abstract

A vehicle fuel tank includes a sensing tube having one end communicating with the tank interior close to the top thereof and a second end extending above the top of the tank and, when a filler pipe 12 is open, communicating with atmosphere. The sensing tube is interrupted within the tank and adjacent the second end at a level above the maximum intended fuel level of the tank so that liquid fuel collecting in the tube can be blown out of the tube by gas flow along the tube. The interruption may be provided by forming the tube as nested sections 24, 26 or by a hole through the tube wall. <IMAGE>

Description

A Fuel Tank This invention relates to a fuel tank having an internal fuel level sensing arrangement.

In order to ensure that a vehicle fuel tank is filled to the designed level with fuel, it is known to incorporate in the tank a so-called sensing tube. The sensing tube vents the top of the tank as the fuel level rises in the tank, but at a pre-determined point the mouth of the sensing tube is blocked by the rising fuel, a volume of air is trapped in an ullage space at the top of the tank and when further fuel is charged to the tank, it will just result in a rapid rise in level in the tank filler pipe, which will in turn activate a shut-off switch in a fuel filler nozzle.

The sensing tube normally extends between the internal cavity of the tank and a position close to the top of the filler pipe, so that when the filler cap is in place both the filler pipe and the sensing tube are closed.

It is known to have a sensing tube which runs externally of the tank and which projects through the tank wall so that the mouth of the sensing tube can be positioned as desired.

This however has the disadvantage that a separate external component is required on the fuel tank, and that an additional seal in the fuel tank wall is required where the sensing tube passes through the wall. Such seals are always vulnerable to leakage.

It is also known in principle to locate the sensing tube internally of the tank, and this is particularly appropriate where the tank has a higher 'dome' remote from the sensing outlet pipe. However internally mounted sensing tubes are prone to filling with fuel, and if the tube does fill with fuel, then it will not perform its function.

According to the present invention, there is provided a motor vehicle fuel tank having a filler pipe through which fuel can be introduced to the tank and a sensing tube which extends within the tank and has a first end communicating with the interior of the tank at a point close to the top of the tank and a second end extending above the top of the tank and, when the filler pipe is opened, communicating with the atmosphere, wherein the sensing tube is interrupted at a point within the tank and adjacent the second end at a level just above the maximum intended fuel level in the tank so that any liquid fuel collecting in the tube can be blown out of the tube by the gas flow along the tube.

The interruption in the sensing tube may take the form of a simple hole through the tube wall at the appropriate position. Alternatively however the tube may be in two nested sections, with the upper section being of larger diameter than the lower section and the lower section terminating, within the upper section, at the position just above the maximum intended fuel level in the tank.

Because of the interruption in the sensing tube, the gas pressure present in the ullage space during filling will have no difficulty in blowing out any liquid fuel trapped in the sensing tube, since this liquid fuel only has to be lifted through a relatively small head.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a fuel tank in accordance with the invention; Figure 2 is a side view of an alternative form of fuel tank in accordance with the invention; and Figure 3 shows a detail of part of the fuel tank.

Figure 1 shows a fuel tank 10 with a filler neck 12. A petrol pump filler nozzle 14 is shown in position discharging fuel into the tank. The tank 10 has two turrets 16, 18 both of which have to be filled with fuel whilst leaving an ullage space 20 at the top. This ullage space is required to allow for expansion of the fuel under different atmospheric conditions.

The tank includes a sensing tube which has an upper section 24 and a lower section 26. In use, whilst the tank is being filled and whilst the fuel level is below the dotted line 22, air will escape from the tank through the upper section of the sensing tube 24. However once the level rises above the dotted line 22, the turret 16 will be isolated from the upper sensing tube section 24, and air can then only escape from the turret 16 through the lower section 26 of the sensing tube, and from the lower section 26 through the upper section 24. When the fuel level in the turret 16 rises to the top of the sensing tube section 26, then fuel will flow in and fill up the lower section 26, but as soon as this section is full there will be no possibility of air escaping from the ullage space 20, and the maximum fuel level will have been reached.

At the same time, the fuel level in the turret 18 will reach the upper edge of the lower opening of the upper section 24, so that an air volume is at the same time trapped in the turret 18.

When fuel is used up from the tank, the fuel level will drop again. However the fuel which has flowed into the lower section 26 of the sensing tube will be trapped there and will remain in the sensing tube even when the fuel level drops very low.

When the tank is refilled, and when the fuel level rises above the dotted line 22, then the trapped air volume in the turret 16 will be compressed as the fuel level continues to rise. The compression of the air will produce enough pressure to force the fuel in the sensing tube section 26 out through the top of the tube section at 28, and this fuel will then return to the tank. The tube section 26 will then be unobstructed and will allow gas to escape to atmosphere until the maximum fuel level is reached.

The sensing tube section 26 is secured to a top wall of the tank by a bond shown at 30.

Because the liquid fuel can drain back into the tank from the open end 28 of the lower tube section 26, only a small pressure head (equal to the distance A) is required to clear the tube of liquid fuel. It is preferred that the open end 28 of the tube section 26 be level with or very slightly higher than the opposite end of the tube section, in the turret 16.

Figure 2 shows an alternative embodiment which acts in a similar way. However in this case there is only one isolated turret 16 in the fuel tank 10.

Figure 3 shows a detail of the part of the sensing tube which is interrupted, ie where the lower section 26 is housed within the bottom end of the upper section 24.

Whilst the remote turret 16 is being filled with fuel, air will be escaping from the second turret 18 directly into the upper tube section 24, along the path indicated by the arrows 32 in Figure 3. This air flow can create a venturi effect which will help to expel liquid fuel from the lower tube section 26.

In the embodiment shown, the interruption of the sensing tube takes the form of one tube section being housed within another tube section. However other types of interruption are possible; for example there may be a continuous sensing tube with a hole through the wall at a position approximately the same as the position of the top end 28 of the lower sensing tube section 26, shown in Figure 1.

The invention makes it possible to use an internal sensing tube in a tank, which has advantages in fuel tank integrity and lack of external obstructions on the tank surface, whilst avoiding the drawback of having a sensing tube which may fill up with liquid fuel. If the tube does fill with liquid fuel and cannot easily be drained, unpredictable filling characteristics result such as premature cut-off of the fuel pump nozzle 14.

Claims

1. A motor vehicle fuel tank having a filler pipe through which fuel can be introduced to the tank and a sensing tube which extends within the tank and has a first end communicating with the interior of the tank at a point close to the top of the tank and a second end extending above the top of the tank and, when the filler pipe is opened, communicating with the atmosphere, wherein the sensing tube is interrupted at a point within the tank and adjacent the second end at a level just above the maximum intended fuel level in the tank so that any liquid fuel collecting in the tube can be blown out of the tube by the gas flow along the tube.

2. A fuel tank as claimed in Claim 1, wherein the interruption in the sensing tube takes the form of a simple hole through the tube walL at the position just above the maximum intended fuel level in the tank.

3. A fuel tank as claimed in Claim 1, wherein the tube is in two nested sections, with the upper section being of larger diameter than the lower section and the lower section terminating, within the upper section, at the position just above the maximum intended fuel level in the tank.

4. A motor vehicle fuel tank, substantially as herein described with reference to the accompanying drawings.