GB2273562A

GB2273562A - Fuel level indicator

Info

Publication number: GB2273562A
Application number: GB9226503A
Authority: GB
Inventors: Ronald Peter Pardy
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1992-12-19
Filing date: 1992-12-19
Publication date: 1994-06-22
Also published as: GB9226503D0

Abstract

A fuel level indicator uses a signal tube 22 which extends from the bottom to the top of the fuel tank and which is connected at the bottom end into the suction side of the fuel pump 16. The signal tube 22 has a set of small holes through the walls of the tube, over the height of the tube. When the pump is running, a depression is produced in the signal tube 22 and the magnitude of this depression will vary in accordance with how many of the holes 34 are above rather than below the level of the fuel 14. The vacuum signal from the tube 22 can then be used to produce a reading on a gauge indicative of the fuel level in the tank. <IMAGE>

Description

FUEL LEVEL INDICATOR This invention relates to a fuel level indicator for indicating the fuel level in a motor vehicle fuel tank. The invention is specifically concerned with installations where fuel is pumped to a motor vehicle engine from a fuel tank by means of a constant speed, in-tank pump. Such pumps are commonly used to feed fuel injected engines.

Convention fuel level indicator assemblies make use of a float arm pivoted to a gauge body. Movement of the float arm follows changes in the fuel level in the tank causing a contact to move over a resistor track which then produces an indication of the fuel level in the tank. Such assemblies are complex to construct and are vulnerable to damage, particularly during storage and assembly.

There have also been a number of proposals for linear fuel level gauges, but none of these have yet found ready acceptance.

According to the present invention, there is provided a motor vehicle fuel tank incorporating means for indicating the fuel level in the tank, the tank containing a constant speed, in-tank fuel pump for pumping fuel to an engine, the pump having a fuel intake and a siganl tube connected to the intake and extending from the bottom of the tank to the top, the tube having a plurality of holes through the wall thereof and the tube bore being connected to a vacuum gauge so that the deflection on the vacuum gauge is proportional to the fuel level in the tank.

The holes through the tube wall will preferably be arranged at regular spacings over the height of the tank. The invention makes use of the fact that suction in the tube will more readily draw air into the tube through the holes that are above the fuel level than it will draw fuel through the holes that are below the fuel level. When the tank is full a relatively small number of holes will be surrounded by air and a relatively large number will be surrounded by fuel. When the pump is operating, there will be a relatively high vacuum in the tube because only a small quantity of air can be drawn in. In contrast however when the tank is nearly empty most of the holes will be surrounded by air and only a few will be surrounded by fuel.

The depression produced in the tube through operation of the pump will therefore be quickly equalised by air drawn into the tube at all the exposed holes. When the tank is nearly empty the vacuum level will therefore be low. As the fuel level varies between these two extremes, a varying vacuum will be experienced in the tube.

This vacuum level can be displayed directly on a gauge, and the gauge may be calibrated to directly indicate the tank fuel level. Alternatively however the vacuum signal can be used to produce an electrical signal indicative of the vacuum level, and this electrical signal can be compensated, for example for variations in temperature or in pump speed, before being used to indicate fuel level.

The pump preferably has a main fuel intake independent of the tube so that the main intake of fuel is directly from the tank with only a minor proportion reaching the pump from the tube.

The holes through the signal tube may be, for example, approximately O.lmm in diameter.

Where the fuel tank has an irregular shape, the vertical spacing of the bleed holes can be set in accordance with the shape of the tank to give a linear relationship between the output reading and the tank content.

The invention also provides a constant speed, in-tank fuel pump for pumping fuel to an engine, the pump having a fuel intake and a signal tube connected to the intake and extending from the bottom of the tank to the top, the tube having a plurality of holes through the wall thereof and the tube bore being adapted to be connected to a vacuum gauge.

The invention will now be further described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a schematic drawing showing a fuel tank installation in accordance with the invention; and Figure 2 is a detail view of part of the installation of Figure 1, on a larger scale.

Figure 1 shows a fuel tank 10 with a filler neck 12 closed by a cap 14. The tank 10 is shown partly filled with fuel 14, and inside the tank a fuel pump 16 is fitted. The pump 16, which is electrically driven, draws fuel in from the tank through the base of the pump and pumps it through a fuel feed line 18 to an engine (not shown). To enable the pump to run at a constant speed with a constant fuel delivery rate whatever the speed/load of the engine, it is arranged that a proportion of the fuel pumped returns to the tank through a fuel return line 20.

The components so far described are conventional and appear in existing fuel tanks.

In order to measure the amount of fuel 14 left in the tank, the invention provides a signal tube 22 which extends from the bottom to the top of the tank and is connected at the lower end to the pump 16. Where the signal tube 22 leaves the tank 10, it is connected by a pipe 24 to a vacuum measuring module 26, and a signal is output from this module to a gauge 28.

The manner in which this signal tube and the vacuum module are able to monitor the fuel level, and thus the fuel content in the tank will now be described with reference to Figure 2. It will be seen from this Figure that the signal tube 22 which extends from the bottom 30 to the top 32 of the tank has a series of small holes 34 formed in it. These holes are provided at regular intervals over the height of the tube 22 and have a diameter of, say, O.lmm. The bottom end of the tube 22 is connected into the suction side of the pump 16. The actual size of the holes 34 will be determined by experiment and may be greater or less than O.lmm.

When the vehicle in which the tank is installed is stationary with the engine off, the fuel level inside the tube 22 will flow through the holes 34 and will reach equilibrium with the fuel in the rest of the tank.

When the engine is turned on, the pump 16 begins to operate and sucks fuel in from its lower side and through the tube 22. This suction will cause the fuel level inside the tube 22 to be lowered. As the liquid level inside the tube drops, so there will be a reduction in pressure in the space inside the tube, above the liquid. This reduction in pressure will be transmitted along the pipe 24 to the vacuum module 26. However because there will now be a lack of equilibrium between the air space 36 in the tank and the air space above the liquid in the tube 22, air will rush from the tank 36 through the holes 34 into the tube 22. The holes 34 are however small, and the size of the holes is chosen so that the rate at which air flows in will be less than the rate at which fuel is pumped out by the pump 16.

In fact, the rate at which air will flow into the tube 22 will be directly proportional to the number of holes 34 which are above the liquid level. If the tank is full so that all of the holes 34 are below the liquid level, the level of depression sensed by the vacuum module 26 will depend entirely on the rate of working of the pump 16.

However as soon as one hole is uncovered, air will start to flow into the tube and air will flow in faster and faster as more and more holes are uncovered. Finally, when all of the holes are uncovered and air can flow into the tube through all of them simultaneously, the depression measured by the module 26 will be a minimum.

Between the vacuum module 26 and the output gauge 28 there may be additional electronic circuitry to compensate for different ambient temperatures, different ambient pressures and for voltage variation driving the pump 16 which may result in alterations in pump speed, and also to compensate for fuel slosh.

The signal tube 22 does not have to run vertically through the tank although it must extend from the tank bottom to the tank top. The vertical spacing between the holes 34 does not have to be regular. If the tank has a larger volume near the top than near the bottom, then it may be possible to place the holes 34 closer together near the top and further apart near the bottom, to provide a linear output.

The signal tube 22 can be provided as a sub-assembly with the pump 16 and the sub-assembly can be mounted as one into the tank 10.

The vacuum module 26 may also have a reference pressure provided to it via a reference pipe (shown in dotted lines 38 in Figure 1) to provide an additional data input.

Claims

1. A motor vehicle fuel tank incorporating means for indicating the fuel level in the tank, the tank containing a constant speed, in-tank fuel pump for pumping fuel to an engine, the pump having a fuel intake and a siganl tube connected to the intake and extending from the bottom of the tank to the top, the tube having a plurality of holes through the wall thereof and the tube bore being connected to a vacuum gauge so that the deflection on the vacuum gauge is proportional to the fuel level in the tank.

2. A fuel tank as claimed in Claim 1, wherein the holes through the tube wall are arranged at regular spacings over the height of the tank.

3. A fuel tank as claimed in Claim 1 or Claim 2, wherein the vacuum gauge is calibrated to directly indicate the tank fuel level.

4. A fuel tank as claimed in Claim 1 or Claim 2, wherein the vacuum gauge produces an electrical signal indicative of a vacuum level, and and electronic circuitry is provided to modify this signal before it is used to indicate the tank fuel level.

5. A fuel tank as claimed in any preceding claim, wherein the pump has a main fuel intake independent of the tube so that the main intake of fuel is directly from the tank with only a minor proportion reaching the pump from the tube.

6. A fuel tank as claimed in any preceding claim, wherein the holes through the signal tube are approximately 0.lmm in diameter.

7. A fuel tank as claimed in Claim 1, wherein the fuel tank has an irregular shape, and the vertical spacing of the bleed holes is set in accordance with the shape of the tank to give a linear relationship between the output reading and the tank content.

8. A constant speed, in-tank fuel pump for pumping fuel to an engine, the pump having a fuel intake and a signal tube connected to the intake and extending from the bottom of the tank to the top, the tube having a plurality of holes through the wall thereof and the tube bore being adapted to be connected to a vacuum gauge.

9. A fuel tank substantially as herein described with reference to the accompanying drawings.

10. A fuel pump substantially as herein described with reference to the accompanying drawings.