TECHNICAL FIELD

The present invention relates to fuel delivery systems, and specifically to pressure regulating means for duel delivery systems for common rail fuel injection systems, such as diesel fuel injection systems.

BACKGROUND OF THE FNVENTION

A known fuel delivery system for a common rail application, such as a single plunger common rail diesel pump application, comprises a low pressure regulator which controls a return flow of fuel from a cambox to a fuel tank, and a separate venturi, which creates a depression, i.e. a reduction in pressure, for an injector leak return flow path. A fuel flow through the venturi alters depending on an opening/closing function of the regulator. The separate low pressure regulator and venturi of prior art pumps requires multiple internal drillings, and a relatively large pump envelope to accommodate the two separate components.

SUMMARY OF THE FNVENTION

It is an object of the present invention to provide an improved fuel delivery system which at least mitigates the above mentioned problems.

Accordingly the present invention provides, in a first aspect, pressure regulating means according to claim 1.

The pressure regulating means comprises a piston located for reciprocating movement within an outer body of integral component; wherein fuel from the second inlet fuel flow enters a recess of the pressure regulating means via an entry port; wherein the piston is biased by a spring into a closed position in which an exit flow of fuel from the recess to the back-leak fuel flow path is prevented via at least one regulated flow port is prevented, and wherein an exit fuel of fuel from the recess to the back-leak fuel flow path via at least one back-leak return port is enabled; and wherein at a predetermined inlet fuel pressure, the piston is urged against the biasing of the spring into a fully open position, in which exit fuel flows from the recess to the back-leak flow path via the each or regulated flow port and via the or each back-leak return port are enabled; Preferably, the recess is defined within the piston and the spring is provided in a spring chamber, wherein the recess and the spring chamber are separated by a wall of the piston, the pressure regulating means further comprising a damping orifice providing a flow path between the spring chamber and the back- leak return flow path; wherein the spring chamber and the damping orifice act as damping means to damp the movement of the piston.

The venturi may comprise a gap in an internal annular projection provided in the piston. In a further aspect, the present invention comprises a fuel delivery system for an internal combustion engine comprising pressure regulating means in accordance with the above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of an fuel delivery system in accordance with a first embodiment of the present invention; Figure 2 is a cross-sectional view of a combined low pressure regulator/venturi component in accordance with the first embodiment of the present invention; Figure 3 is a schematic representation of a fuel delivery system in accordance with a second embodiment of the present invention; and Figure 4 is a cross-sectional view of a combined low pressure regulator/venturi component in accordance with the second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, a venturi is incorporated into a low pressure regulator piston, to form a single pressure regulating component.

Referring to Figure 1, pressure regulating means comprising a combined low pressure regulator/venturi unit 100 in accordance with a first embodiment of the present invention, is illustrated schematically as part of a fuel delivery system 2. Fuel such as diesel is supplied, at low pressure, from a fuel supply comprising a fuel tank 10, to a cambox 12. From the cambox 12, fuel is provided along a first inlet fuel flow path 6, via a filter 14, an inlet metering valve 16 and an inlet valve 18, to a pumping chamber 20. The fuel is subsequently pressurised to a high pressure in the pumping chamber 20, and the high pressure fuel is supplied along a high pressure fuel path 32, via an outlet valve 22 and common rail accumulator volume 24, to one or more injectors 26.

A second inlet flow path 8 is also provided from the cambox 12; the second flow path 8 provides fuel, at an inlet pressure, to the regulator/venturi unit 100. The regulator/venturi unit 100 regulates the pressure of this return flow of fuel, thereby controlling the average fuel pressure within the cambox. After exiting the combined regulator/venturi unit 100, a flow of fuel at a back- leak pressure returns to the fuel tank 10 along a back-leak return flow path 30.

The regulator/venturi unit 100 also receives a back- leak flow of fuel from the injectors 26, via an injector back-leak flow path 32. The venturi acts upon this injector back-leak flow, and it is subsequently also returned to the fuel tank 10 via the back-leak return flow path 30.

The operation of the regulator/venturi unit 100 is described in greater detail below.

Referring to Figure 2, the combined regulator/venturi unit 100 of a first embodiment of the present invention comprises an outer body 102, in which an internal member comprising a piston 104 is arranged for reciprocating movement therein. An interior of the piston 104 defines a recess 106.

The regulator/venturi unit 100 comprises a first, entry end 108, and distal from the first end 108, a second end 110, towards which a spring chamber 120 is provided. The spring chamber 120 is separated from the recess 106 of the piston 104 by a radial wall 112 of the piston. Biasing means comprising a coil spring 122 is provided in the spring chamber 120; the spring 122 abuts a first spring seat 124 provided by an internal face 162 of a radial wall 160 of the outer body 102 defining the second end 110 of the unit 100, and a second spring seat 126 provided by an end face 116 of the piston 104.

The piston 104 comprises an internal orifice 130, formed by gap in an annular internal projection 118.

The regulator/venturi unit 100 comprises an entry port 134 at the entry end 108, for receiving fuel from the second inlet flow path 108 from the cambox 12. A plurality of ports are provided through the outer body of the unit 100: regulated flow ports 140, 142 are provided towards the first end 108 of the unit 100, a back- leak return port 144 is provided towards the second end 110 of the unit 100, and a venturi port 132 is at a position axially between the regulated flow ports 140, 142 and the back- leak return port 144.

In the first embodiment of the present invention, back- leak return port 144 is provided in an axial side wall 166 of the outer body of the regulator/venturi unit 100. Additionally, a damping orifice 146 is provided through the outer body

102 of the regulator/venturi unit 10 towards the second end 110, providing a damping flow path between the spring chamber 120 and the back-leak return flow path 30. Fuel from the second inlet flow path 8 from the cambox 12 flows, at the inlet pressure, via the entry port 134, into the recess 106 of the regulator/venturi unit 100. Under the pressure of the fuel entering the regulator/venturi unit 100 and as described in greater detail below, the piston 104 is moveable between a fully open position and a fully closed position. In the fully open position, as shown in Figure 2, the piston 104 is at a lowermost position (in the orientation of Figures 1 and 2), and in the closed position, the piston 104 is at an uppermost position.

The piston 104 is biased into the fully closed position by the spring, i.e. the spring 122 biases the piston away from the internal end face 162 of the outer body 102 of the unit 100. In the fully closed position, the regulated flow ports 140, 142 are sealed by an external surface of a top section 168 of an axial wall 164 of the piston 104, thereby closing the flow path out of the recess 106 via the regulated flow ports 140, 142.

In the fully closed position, a fuel flow path is enabled through the venturi port 132, via a corresponding venturi port 170 provided in the axial side wall 166 of the piston 104, into a venturi section 172 of the recess 106. This flow creates a depression which is enabled by cut-outs 152, 154 provided in the external wall 164 of the piston 104 above and below the venturi port 170, which prevent the external wall 164 from sealing the venturi port 132 of the outer body 102. Accordingly, the venturi ports 132, 170 still act to reduce the pressure of the injector back flow received into the recess 106 to the predetermined level. Similarly, a flow path is enabled out of the recess 106 through the back-leak return port 144, via a corresponding back-leak return port 172 provided in the axial wall of the piston 104, by virtue of further cut-outs 156, 158 provided in the external wall 164 of the piston 104 above and below the back- leak return port 172, which prevent the external wall 164 from sealing the back-leak return port 144.

Fuel entering the recess 106 from the injector back- leak flow path 32 via the venturi ports 132, 170 is at a higher pressure than the inlet pressure. The venturi ports 132, 170 create a depression in the injector return flow, thereby reducing the pressure of the injector return flow of fuel, to a predetermined level.

Fuel entering the recess 106 via the entry port 134, will be at the inlet pressure, as determined by pressure of fuel exiting the cambox 12. Accordingly, a force provided to the piston 104 by the fuel entering the recess 106 will be dependent upon the magnitude of the inlet pressure.

If the force applied to the piston 104 by the inlet fuel pressure is less than the force applied to the piston 104 by the spring 122, the piston 104 will not move and will remain in the fully closed position, wherein fuel cannot flow out of the recess through the regulated flow ports 140, 142.

At and above a predetermined inlet fuel pressure, the force applied to the piston 104 will exceed the biasing force of the spring 122. The piston 104 is then urged, along a longitudinal axis A of the regulator/venturi unit 100, towards the internal end face 162 of the outer body 102, i.e. the piston 104 is urged from the fully closed position to the fully open position in which fuel can flow out of the regulated flow ports 140, 142. In the orientation of Figure 2, the piston 104 is pushed downwardly. The spring chamber 120 and the damping orifice 146 act as a damping mechanism to damp movement of the piston 104 towards the internal end face 162 of the outer body 102.

When the piston 104 is in the fully open position, the regulated flow ports 140, 142 are no longer obstructed/sealed by the external wall 164 of the piston 104, and therefore an additional flow path is enabled from the cambox 12 to the back-leak return flow path 30, through the regulated flow ports 140, 142, i.e. in the open position, fuel exits to the back-leak return flow path 30, via the regulated flow ports 140, 142 in addition to the back-leak return port 144.

When the piston 104 is in the fully open position the flow path into the recess 106 from the injector back- leak flow path 32 is maintained through the venturi ports 132, 170, and the venturi ports continue to reduce the pressure of the flow received from the injector return flow path 32 to the predetermined back-leak pressure.

Fuel exiting the recess 106 of the regulator/venturi unit 100, via the back- leak return port 144 (when the piston 104 is in the closed position) or via both the back-leak return port 144 and the regulated flow ports 140, 142 (when the piston 104 is in the open position), is returned to the fuel tank 10, via the back-leak return flow path 30, at the predetermined back-leak pressure. When the piston 104 is at a partially open position, i.e. between the fully open and fully closed positions, a partial flow of fuel can exit via the regulated flow ports 140, 142, i.e. a reduced volume of fuel can exit via the regulated flow ports 140, 142 than if the piston 104 was in the fully open position. The regulator/venturi unit 10 acts to regulate fuel pressure within the cambox 12. If the fuel pressure within the cambox 12 is too great, i.e. exceeds a predetermined value, the piston 104 is caused to move to the open position and allow more fuel to flow through to the back-leak return path 30, thereby reducing the fuel pressure within the cambox 12 to the predetermined pressure. Accordingly, the selected predetermined average fuel pressure is maintained in the cambox 12. The opening pressure for the regulator/venturi component 100, i.e. the pressure at which the piston 104 is caused to move towards the fully open position, is determined by the size of the piston internal orifice 130, the rate and pre-load of the spring 122, the positions of the regulated flow ports 140, 142, and the size of the damping orifice 146. These parameters are therefore selected according to the required predetermined average fuel pressure of the cambox 12.

Furthermore, the size of the internal orifice 130 is selected to allow the correct volume of fuel through the venturi section 172 to obtain the necessary reduction to a regulated pressure setting.

Referring to Figure 3, a combined low pressure regulator/venturi unit 200 in accordance with an alternative, second embodiment of the present invention is illustrated schematically as part of a fuel delivery system 202 in Figure 3. The alternative regulator/venturi unit 200 is illustrated in isolation in Figure 4, in a fully open position.

In common with the first embodiment, the second embodiment comprises a combined regulator/venturi unit 200 comprising a piston 204 which is arranged for reciprocating movement within the outer body 202 of the regulator/venturi unit 200.

However, in the second embodiment, the piston 204 does not include a radial wall to separate the recess 206 from the spring chamber. Accordingly, the recess 206 comprises the internal area defined within piston 106, and also the spring chamber area. In the second embodiment, the back-leak return port 244 is located in the radial wall 260 of the outer body 202 of the regulator/venturi unit 200 which defines the second end 210 of the unit 200, remote from the first, entry end 208. As the second embodiment does not include a separated spring chamber or damping orifice extending therefrom, opening of the piston, i.e. movement of the piston 204 towards the internal end face 262 of the outer body 202, is not damped.

In common with the first embodiment, when the piston 204 is in the closed position, the regulated flow ports 240, 242 are sealed by an external surface of a top section 168 of an external wall 264 of the piston 204 however fuel can flow through the back-leak return port 244, and when the piston 204 is in the open position, fuel can flow from the recess 206 through both the back-leak return port 244 as well as through the regulated flow ports 240, 242.

The second embodiment therefore allows fuel flow to pass through the regulator/venturi unit 200 with less restriction on the downstream side (i.e. towards the second end 210 of the unit 200) of the venturi ports 232, 270.

In both embodiments of the present invention, the pressure of fuel flowing through the venturi is more consistent than in prior art embodiments, as it is incorporated in the regulator. Accordingly, a more consistent depression in fuel pressure is generated by the venturi than in prior art embodiments.

The present invention reduces the number of internal drillings required compared to prior art embodiments. Furthermore, combining the venturi and regulator into one component also allows for a reduced overall pump packaging size compared to prior art embodiments. REFERENCES fuel delivery system 2

first inlet flow path 6

second inlet flow path 8

fuel tank 10

cambox 12

filter 14

inlet metering valve 16

inlet valve 18

pumping chamber 20

outlet valve 22

common rail accumulator volume 24 injectors 26

high pressure fuel path 28 back-leak return flow path 30 injector back-leak flow path 32 regulator/venturi unit 100, 200 outer body 102, 202

piston 104, 204

recess 106, 206

unit first, entry end 108, 208 second end 110, 210

piston radial wall 112, 212 end face of the piston 1 16 piston annular internal projection 118 spring chamber 120

spring 122

first spring seat 124

second spring seat 126

outer body venturi orifice 130 venturi port 132, 232

entry port 134 regulated flow ports 140, 142, 240, 242

outer body back-leak return port 144, 244 damping orifice 146

piston cut-outs (venturi area) 152, 154

piston cut-outs (back-leak return port area) 156, 158 outer body radial wall 160, 260

internal end face of outer body 162, 262

piston axial external wall 164, 264

outer body side wall 166

axial external wall top section 168

piston venturi port 170

piston back leak return port 172

venturi portion 174

unit longitudinal axis A