Fuel consumption measuring system for an internal combustion engine powered vehicle

The accurate measurement of fuel flow to the engine of a road vehicle which incorporates a fuel system where excess fuel is drawn from the fuel tank and subsequently returned to the tank is made very difficult by such excess fuel flow. Although accurate measurements can be made in these circumstances, measurement systems proposed in the past have been complicated suitable for use only in special test vehicles, rather than as standard equipment in production vehicles.

It is an object of the present invention to provide a fuel flow measuring system for such an application in a convenient form.

A fuel flow measuring system in accordance with the invention comprises the combination of a return fuel storage tank mounted in the main fuel tank, means sensitive to the level of fuel in the return fuel storage tank, means operable by said level sensitive means for varying the ratio of the quantity of fuel drawn from the main tank to the quantity of fuel drawn from returned fuel so as to maintain the level in the return fuel storage tank constant, and a flow measuring device connected to measure only the quantity of fuel drawn from the main tank.

The means operable by the level sensing means may be a proportioning valve with one input connection from the return fuel storage tank and another input connection via the flow measuring device from the main tank. The proportioning valve is arranged to cut off flow from the return fuel storage tank as the level therein falls and cut off flow from the main fuel tank as the level in the return fuel storage tank rises.

Alternatively, the means operable by the level sensing means may be a pump operating to transfer fuel from the main tank to the return fuel storage tank via the flow measuring device.

In the accompanying drawings:-

• Figure 1 is a view, partly in section, of a main fuel tank with one example of a measuring system in accordance with the invention installed therein;
• Figure 2 is an enlarged sectional view of valve means forming part of the system; and
• Figure 3 is a view like Figure 1 showing another example of the invention.

As shown in Figure 1, the main fuel tank 10 has a return fuel storage tank 11 mounted in it. The tank 11 provides a completely isolated air tight enclosure, although a venting valve 12 is arranged to interconnect the upper extremity of the tank 11 to the lowest part of tank 10, flow of air and vapour from the tank 11 to the tank 10, being permitted by the valve 12, in the event of the ambient or fuel temperature rising for any reason or to get rid of any fuel-entrained air and vapour.

The tank 11 is connected by a pipe 13 extending through the tank 10 to a connector 14 whereby it is connected to the fuel return line of the petrol.injection or diesel injection system of the vehicle in which the tank is installed. The return line receives excess fuel drawn from the tank(s) by the pump of the fuel system, but spilled by the pressure regulating valve or circulation circuit of that system. A baffle 15 is mounted in the tank 11 to separate the part of the tank 11 which the pipe 13 enters from a part thereof in which a float 16 is mounted. The float 16 is connected to a proportioning valve 17, shown in more detail in Figure 2, which controls the ratio in which fuel is drawn from the two tanks to maintain the level of fuel in the tank 11 constant. The baffle 15 prevents the float 16 from being perturbed by return fuel flow into the tank 11.

The valve 17 has an inlet 18 connected by a fuel flow metering device 19 and a pipe 20 with a strainer 21 thereon to the main fuel tank. The float 16 is connected to a vertically movable valve element 22 including an upper valve portion 22a and a lower valve portion 22b. The upper portion 22a controls flow from the tank 11 into an outlet gallery 23 of the valve and the portion 22b controls flow frow the inlet 18 to the gallery 23. As the float rises portion 22a lifts from its seat and permits progressively more flow from the tank 11, and the portion 22b progressively impedes flow from the inlet 18.

The valve 17 also has an emergency valve element 24 which is spring-loaded shut and controls a second inlet pipe 25 having a second strainer 26 thereon. The valve 24 opens if the device 19 or the proportioning valve fail, so that the engine can continue to run.

Turning now to Figure 3, in the embodiment shown therein the output from the tank assembly is taken only from the return fuel storage tank. The float 16 operates a valve 30 which controls the output from a pump 31 drawing fuel via filter 22 and delivering it to the flow measuring device 19 from the main tank. The valve 30 controls admission of fuel to the return fuel storage tank, so as to keep the level in the latter by making up fuel consumed by the engine.

Positioning the tank 11 inside the main tank 10 ensures that the returned fuel is cooled by the main stock of fuel and also makes for simple design of the float/valve arrangement.