Fuel delivery system

Abstract

A fuel delivery system (1,fig.1) comprising a fuel store (5,fig.1) and a fuel pump (2,fig.1) for delivering fuel from said store. The system comprises a return valve 11 having an inlet 19 and an outle

Description

The present invention relates to a fuel delivery system, a valve for use in a fuel delivery system and a vehicle comprising a fuel delivery system. For the supply of a fuel from a fuel store such as a tank to a vehicle engine, a fuel pump is typically used. The fuel pump is typically located within the fuel tank. Depending on the fuel demands of the engine, the speed and / or pressure of the fuel pump can adjusted to ensure that the engine receives a sufficient supply of fuel. In some vehicles, the operating range of the engine is such that the variation in the supply of fuel can be provided by a single pump. However, in high performance engines, there can be a significant difference between the fuel demand of the engine when idling compared to that at full throttle. To address this, often two fuel pumps are provided. One fuel pump may be a lower pressure pump to supply fuel from idle up to a predetermined engine speed. To contend with higher engine demands, a higher pressure pump is provided to supply sufficient fuel when the engine is operating up to full throttle. While such an arrangement is useful, it requires two separate fuel pumps as well as controllers and associated control strategies in order to switch between the two fuel pumps. The present invention seeks to overcome or ameliorate at least to a certain degree the problems associated with the prior art. SUMMARY According to a first aspect of the present disclosure, there is provided a fuel delivery system comprising: a fuel store; a fuel pump for delivering fuel from said fuel store; and a return valve arranged downstream of said fuel pump; said return valve having an inlet and an outlet return opening through which fuel can be returned to the fuel store; the return valve configured to close the outlet return opening when the pressure of fuel at the inlet is above a predetermined level and to open the outlet return opening when the pressure of fuel at the inlet is below a predetermined level. Such a system allows the fuel pump to operate within a more optimal range when the pressure of fuel is low, for example, during engine idling. Optionally, said return valve has a biased closure configured to close the return valve opening when the pressure in said return valve inlet is above a predetermined level. A biased closure can be a mechanical means to control the opening and closing of the return valve. The biased closure can be configured to close the return valve when the pressure at the inlet is above a pre-determined level. This pre-determined level may be above a set fuel supply for the engine. Optionally, said return valve has a biased closure configured to open the return valve opening when the pressure in said return valve inlet is below a predetermined level. The biased closure can be configured to open the return valve when the pressure at the inlet is below a pre-determined level. This pre-determined level may be at a level below which the pump could stall. Optionally, the biased closure comprises a spring. The spring may be a coiled spring. A sprung plate or other biasing means could also be used. The spring rate of the spring can for example be determined by using the surface area of biased closure in contact with the fluid at the inlet, such as the surface of the spherical ball to calculate the necessary spring force to resist closing of the valve at a predetermined pressure. Optionally, the biased closure comprises a spherical ball around which fluid may pass when the return valve opening is open. Aspherical ball can fit within the valve and engage with the biasing element such as a spring. The return valve is configured to provide a predetermined flow rate when in its open position. This can be achieved by the gap or spacing provided, for example, around the spherical ball, having a predetermined flow cross-section. Optionally, the return valve comprises an annular seat with a corresponding internal spherical cap to receive said spherical ball. Such a form of spherical cap provides an effective fluid seal for the return valve in the closed position or state. Optionally, a ring is provided to contain said biased closure. The ring can sit within a groove in the return valve. Such an arrangement allows for ease of assembly. According to a second aspect of the disclosure, there is provided a valve comprising an inlet and an outlet return opening, said valve having a biased closure configured to close said outlet return opening when the pressure at said valve inlet is above a predetermined level. The valve can be configured to open and close at predetermined pressures at the inlet. Optionally, said biased closure is configured to open said outlet return opening when the pressure at said valve inlet is below a predetermined level. Optionally, the biased closure comprises a spring. The spring may be a coil spring to apply a closing force on said biased closure to the valve. Optionally, the biased closure comprises a spherical ball. Optionally, the valve comprises an annular seat with a corresponding internal spherical cap to receive said spherical ball. The surface provided by the spherical cap provides a fluid seal when the valve is in its closed position. Optionally, a ring is provided to contain said biased closure. Such a ring facilitates the assembly of the valve. Optionally, the valve comprises one or more external circumferential ribs for coupling with a fluid hose. The valve may be machined from any suitable material such as 350 brass. A nickel plate may be applied. According to a third aspect of the disclosure, there is provided a vehicle comprising a fuel delivery system according to the first aspect and / or a valve according to the second aspect and any optional feature thereof. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described purely by way of example with reference to and as illustrated in the accompanying drawings in which: Figure 1 is a schematic drawing of a fuel delivery system; Figure 2 is an image of a valve with a biased return opening; Figure 3 is a schematic cross-section of the valve of Figure 2 in an open position; Figure 4 is a schematic cross-section of the valve of Figure 2 in a closed position; Figure 5 is a cross-section of the valve of Figure 2 in an open position; Figure 6 is a cross-section of the valve of Figure 2 in a closed position; and Figure 7 is an example duty cycle chart of the fuel delivery system of Figure 1. DETAILED DESCRIPTION Figure 1 shows a schematic drawing of a fuel system generally at 1. The fuel system comprises a tank 5 for holding a liquid fuel such as gasoline. A high-speed pump 2, for example, a 16 turn high flow, high pressure screw pump operating at over 500l / hr and at 8 bar, is provided within the tank. However, the pump could be located in-line outside of the tank. The pump 2 is arranged within a retaining pot 4 above the internal surface of the tank 5 which prevents fuel starvation to the pump. A strainer 3 is provided before the pump 2 to avoid debris, such as particulate matter or other impurities from flowing into the pump and causing damage to the pump 2 and / or the vehicle engine. Fuel from the pump 2 passes initially through check valve 6 to fuel line 7. Fuel then passes through a secondary filter 8 before the fuel line passes through flange 9 to be delivered via fuel line 10 to the vehicle engine or fuel rail. A return valve 11 is fluidly coupled to the fuel line before it passes through the flange 9. The valve 11 comprises a biased closure, which is designed to close the return valve 11 when the pressure in the fuel line 7 at the return valve inlet 19 is above a pre-determined value. The return valve 11 may be fluidly coupled to the fuel line 11 via a T-junction. The return valve 11 may be formed integrally with a T-junction for fluid connection to the flow line 7. When the pressure in the fuel line 7 at the return valve inlet 19 is below a pre-determined value, for example, when there is a low fuel demand, e.g. when the engine is idling, the biased closure is biased into an open position such that a proportion of fuel passes to return line 12 back to the retaining pot 4 rather than flowing to the engine. This allows the pump to run at higher speeds and nearer to its optimal operating range even when the fuel demand of the engine is low. To ensure fuel within the tank is within the retaining pot, one or more jet pumps 13,14 may be provided to direct fuel to the retaining pot. The jet pumps 13, 14 operate with fuel from the outlet of the pump 2. Anti-siphon valves 17, 18 may be provided before the jet pumps 13, 14. Additional strainers 15, 16 may be provided to ensure fuel directed using the jet pumps 13, 14 is free from particulates. Figure 2 shows an external view of valve 11 as described in Figure 1. Externally, the valve 11 comprises a generally cylindrical body 22 with, in the example, two circumferential ribs 21 to facilitate secure coupling with a fuel line such as a hose or a line coupling such as a T-junction. At one end of the valve 11, a biased element, in the example in the form of a spherical ball 20, can sit against the inner edge of a ring 23 around circular inlet aperture 19. The valve 11 and the spherical ball may be machined from 360 brass alloy. A nickel plate may be applied to the brass alloy. The function of the valve 11 will be described with reference to Figures 3 and 4. In Figure 3, the valve is shown in an open state. In this open state, the biasing force of a spring 25 used to bias the spherical ball 20, is greater than the pressure of the fuel in the supply line 24 adjacent the valve 11 at inlet opening 19. This can be the case when the fuel pump is operating at lower flow rates, for example, less than 200 litres per hour and below a pressure of 400 kPa. Fuel then bleeds past the spherical element 20 back into the fuel tank. When the fuel pressure goes above 450 kPa, the fuel pressure overcomes the spring force and the spherical ball 20 closes the valve 11. This closed state of the valve 11 is shown in Figure 4. In the closed state of the valve, there is no bleed back into the fuel tank with all fuel from the pump flowing to the engine. By incorporating the valve 11, the fuel pump can artificially run faster at idle condition. This negates the need to an additional low speed pump to serve the engine at idle and low engine speeds. With a pump designed for high pressure flow rates, in the present example, the pump can typically run at 10,000 revolutions per minute (rpm) when there is a large fuel demand from the engine. If such a pump were to run below 2,000 rpm, for example, to serve the fuel demands when the engine is idling, there is a risk that it will stall. The biasing element, here the spring 20 and its stiffness, is chosen depending on the expected fuel supply requirements such that the valve 11 is closed above a predetermined pressure. The spring rate of the spring 20 can for example be determined by using the surface area of the spherical ball 20 to calculate the necessary spring force to resist closing of the return valve 11 at a predetermined pressure. Figure 5 is a cross-section of the valve of Figure 2 in an open position. The return valve 11 has an internal cylindrical cavity 35 which adjoins an annular recess 36 in which spring 25 is located. The outlet return opening 26 is at the centre of the annular recess. When the spherical ball 20 is biased by the spring towards the inlet opening or aperture 19, a circumferential gap 37 is provided between the inner cylindrical wall of the valve and the spherical ball 20 to allow fuel to pass to the outlet return opening 26. Figure 6 is a cross-section of the valve of Figure 2 in a closed position. When the pressure in the fuel line acts on spherical ball 20 to overcome the spring force of spring 20, the spherical ball 20 is moved to sit on annular seat 27 around the inlet to the outlet return opening 26 to prevent fuel from passing to the outlet 27. The annular seat 27 has a spherical cap surface corresponding to the surface of the spherical ball to provide a seal with the spherical ball 20 when in the closed position. A containment ring 23 with an internal diameter smaller than the spherical ball 20 sits in a groove 39 in order to contain the spherical ball 20. Figure 7 is an example duty cycle chart of the fuel delivery system of Figure 1. The left-hand vertical axis shows flow rate in litres per hour. The right-hand vertical axis shows pressure in kPa. The horizontal axis shows pump speeds in rpm. The area bounded by line 30 shows the zone in which the fuel pump is operating with a low demand, e.g. for engine idling. The area bounded by line 31 shows the zone in which the pump operates at increased demand. As the demand increases and the pump pressure and flow increases, the valve closes as indicated by line 33. During normal engine operating conditions, the pump operates with the valve closed as represented by the zone bounded by line 32.

Claims

1. A fuel delivery system comprising:a fuel store; a fuel pump for delivering fuel from said fuel store;and a return valve arranged downstream of said fuel pump; said return valve having an inlet and an outlet return opening through which fuel can be returned to the fuel store;the return valve configured to close the outlet return opening when the pressure of fuel at the inlet is above a predetermined level and to open the outlet return opening when the pressure of fuel at the inlet is below a predetermined level.

2. A fuel delivery system according claim 1, wherein said return valve has a biased closure configured to close the return valve opening when the pressure in said return valve inlet is above a predetermined level.

3. A fuel delivery system according claim 1 or 2, wherein said return valve has a biased closure configured to open the return valve opening when the pressure in said return valve inlet is below a predetermined level.

4. A fuel delivery system according to claim 2 or 3, wherein the biased closure comprises a spring.

5. A fuel delivery system according to any of claims 2 to 4, wherein the biased closure comprises a spherical ball around which fluid may pass when the return valve opening is open.

6. A fuel delivery system according to claim 5, wherein the return valve comprises an annular seat with a corresponding internal spherical cap to receive said spherical ball.

7. A fuel delivery system according to any of claims 2 to 6, wherein a ring is provided to contain said biased closure.

8. A valve comprising an inlet and an outlet return opening, said valve having a biased closure configured to close said outlet return opening when the pressure at said valve inlet is above a predetermined level.

9. A valve according to claim 8, wherein said biased closure is configured to open said outlet return opening when the pressure at said valve inlet is below a predetermined level.

10. A valve according to claim 8 or 9, wherein the biased closure comprises a spring.

11. A valve according to any of claims 8 to 10, wherein the biased closure comprises a spherical ball.

12. A valve according to claim 11, wherein the valve comprises an annular seat with a corresponding internal spherical cap to receive said spherical ball.

13. A valve according to any of claims 8 to 12, wherein a ring is provided to contain said biased closure.

14. A valve according to any of claims 8 to 13, wherein the valve comprises one or more external circumferential ribs for coupling with a fluid hose.

15. A vehicle comprising a fuel delivery system according to any of claims 1 to 7 and / or a valve according to any one of claims 8 to 14.

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