GB2452955A

GB2452955A - A fuel injector

Info

Publication number: GB2452955A
Application number: GB0718372A
Authority: GB
Inventors: Steven Barraclough; Richard Matthew Hoolahan
Original assignee: Scion Sprays Ltd
Current assignee: Scion Sprays Ltd
Priority date: 2007-09-20
Filing date: 2007-09-20
Publication date: 2009-03-25
Anticipated expiration: 2027-09-20
Also published as: GB0718372D0; GB2452955B

Abstract

A fuel injector assembly comprises a pumping chamber 240 and a piston 10 slidable axially to draw fuel into and force fuel out of the pumping chamber. A fuel inlet passage is provided in the piston via which fuel is delivered into the pumping chamber. A one-way, washer-type inlet valve 11 is mounted in the piston to control flow of fuel into the pumping chamber. The valve comprises a valve seat having a plurality orifices arranged in an annular ring and a moveable valve member engageable with the valve seat to close the apertures in the valve seat, the valve member being annular and having a central aperture through which fluid can flow when the valve is open.

Description

--2452955 Fuel Injector The present invention relates to a fuel injector having a valve, and in particular, a fuel injector having a one-way valve.

It is well known for a fuel injector for an internal combustion engine to have one or more one-way valves to control the flow of fuel. A known valve design comprises a disc-shaped member which is moved on to and away from a valve seat defining a circular aperture. It has been found that such a disc member is subjected to unexpectedly large forces during operation, and through use there is significant wear of the valve seat.

The present invention provides a fuel injector comprising: a housing in which a fuel chamber is formed; a piston which is slidable axially in a bore in the housing to draw fuel into and force fuel out of the fuel chamber; a fuel inlet; a fuel outlet; a one-way inlet valve which allows fuel to be drawn into the fuel chamber from the fuel inlet while preventing fuel being expelled from the fuel chamber to the fuel inlet; a one-way outlet valve which allows fuel to be expelled from the fuel chamber to the fuel outlet while preventing fuel being drawn back into the fuel chamber from the fuel outlet; wherein: the fuel inlet comprises a fuel inlet passage in the piston via which fuel is delivered into the fuel chamber; the one-way inlet valve is mounted in piston to control flow of fuel from the fuel inlet passage in the piston to the fuel chamber; and the one-way inlet valve comprises: a valve seat having a plurality orifices arranged in an annular ring; and a moveable valve member engageable with the valve seat to close the apertures in the valve seat, the valve member being annular and having a central aperture through which fluid can flow when the valve is open.

Thus, the moveable annular disc member has a relatively small surface area, which reduces the forces on it, reducing wear of the valve seat. In addition, this valve has been found to have an increased flow capacity compared to a similarly dimensioned valve with a moveable solid disc member.

The present invention will now be described with reference to the accompanying drawings by way of example only, in which: Figure 1 is a schematic illustration of a fuel injector according to the present invention Figure 2 is a cut-away perspective view of a piston with valve according to a first embodiment of the present invention; Figure 3 is a perspective view of a piston according to a second embodiment of the present invention; Figure 4 is a perspective view of the valve disc for use in either of the embodiments of the present invention; Figure 5 is a cross-section through the piston of Figure 3; Figure 6 is an underneath perspective view of a valve seat for use with the piston of Figures 3 and 5; and Figure 7 is a top perspective view of the valve seat of figure 6; Figure 8a to 8d are a schematic illustration of the fuel injector of Figure 1 in different stages during use.

The present invention relates to a fuel injector having a one-way "washer" valve. The fuel injector is for use in an internal combustion engine comprising a cylinder in which reciprocates a piston, with the cylinder and piston defining between them a combustion chamber. The engine is preferably a simple engine, e.g. a single cylinder engine of, for instance, a lawn mower or other garden equipment.

The engine has a fuel injection system comprising a fuel injector according to the present invention arranged to deliver fuel into an inlet passage upstream of an inlet valve. A throttle valve is placed in the inlet passage to throttle the flow of charge air into the combustion chamber.

Figure 1 shows a fuel injector 219 with a piston body located in a pumping chamber 240. A fuel inlet 242 provides for fuel to enter the fuel injector 219 and flow into a fuel passage passing through the piston body 10. A fuel inlet check valve 11 is situated in the fuel passage.

The fuel inlet check valve 11 is a one-way valve. The fuel inlet check valve 11 can allow the flow of fuel from the piston body 10 to the pumping chamber 240.

A solenoid 232 is provided with a back-iron 233 for pulling the piston body 10 downwardly as shown when energised. A piston spring 234 pushes the piston 10 away from the back-iron 233 when the solenoid is de-energised, in order to expel fuel from the pumping chamber 240.

Fuel is dispensed from the pumping chamber 240 to a fuel outlet 237 via a one-way outlet check valve 238. The operation of the fuel injector 219 will be described further with reference to Figures Ba -8d.

With reference to Figures 2 and 4, the piston body 10 for a fuel injector is shown. The piston body 10 has a one-way valve 11 located at one end. The piston body 10 has a hollow cylindrical section 12 defining an inlet port 13 through which fuel can enter into the piston body 12, and flow to the valve 11.

The piston body 10 has a valve seat 16 with multiple orifices 18 defined in it. The orifices 18 are arranged in an annular ring. There are six orifices 18 shown and each orifice 18 is a circular aperture.

A movable annular valve member 20 is aligned with the orifices 18. The annular valve member 20 can engage the valve seat 16 to close the orifices in the valve seat 16.

The annular valve member 20 is movable into and out of engagement with the valve seat 16. The annular valve member has an aperture 22 though which fuel can flow. The valve member 20 is a flat disc. The central aperture 22 is circular.

A cap 30 is supported on a seat 17 provided on the piston body 10. The cap 30 defines a cylindrical cavity 36 in combination with the valve seat 16. The annular valve member 20 is moveable within the cavity 36 along a longitudinal axis of the cavity 36. The cap 30 has a central orifice 32 for flow of fluid out of the cavity. The cap 30 also has a plurality of orifices 34 in an annular ring spaced radially outwardly from the central orifice 32.

There are six orifices 34 shown. The orifices are arranged such that when the annular valve member 20 engages an underside of the cap 30 the valve member only partly covers the orifices and all the orifices remain in part open to allow flow of fluid. However, a part of the annular valve member is exposed via each orifice to the fluid above the cap so that pressure of the fluid can be applied to the valve member to lift the valve member away from engagement with the cap 30.

Radially extending apertures 14 are provided in the piston 10 to allow for venting of vapour which might otherwise become trapped below the valve seat 16.

In use, the one-way valve 10 is closed when the annular valve member 20 engages the valve seat 16, and overlies the orifices 18. The valve 10 is then opened when the valve member 20 is lifted out of engagement with the valve seat 16. Fuel can then flow through orifices 18 and into the cavity 36. The fuel flows both around the periphery of the annular valve member 20 and through the central aperture 22 in the valve member 20. The central aperture 22 provides an additional flow path compared to a solid disc valve member.

The additional flow path allows a dynamic pressure drop at the centre of the aperture 20 and around the periphery of the member 20. There is large contact area between the annular valve member 20 and the valve seat 16 which reduces wear of the valve seat. The aperture 22 also allows for improved flow capacity of the valve. The fuel is dispensed from the valve through the orifices 32, 34 in the outer disc 30.

The flow through the central aperture 22 also increases the closing force on the valve member when compared with a comparable sized disc with no aperture. The closing force on the non-apertured disc has only static pressure exerted over the middle of the valve member and a dynamic pressure drop only around the periphery. The annular valve member 20 additionally has a dynamic pressure drop occasioned by the flow through the central aperture.

The stroke of movement of the annular valve member 20 is small, typically 60-70 microns.

Figures 3 to 7, show an alternate embodiment of the invention. The functioning of the valve assembly illustrated is the same as described above, but whereas in the above-described embodiment the valve seat 16 is integrally formed in the piston 10 and the cap 30 is a separate component, in the alternate embodiment the cap 130 is an integral part of the piston 100 and the valve seat 116 is formed as a separate component. Figures 3 and 5 show the cap 130 with a central orifice 132 and a ring of orifices 134 surrounding the central orifice 132. Figures 6 and 7 show a valve seat 116 formed as a separate component with a lower face as shown in figure 6 and an annular flange 17' extending around the periphery of the component away from the lower face. The flange 17' has an upper rim which in use will abut an underside surface of the cap 130 and the component will be held in place abutting the undersurface of the cap 130 by a spring which acts through the component 17' to bias the -.7-piston 110 to move within a housing. The cap 130 may be held in place only by the spring which also causes movement of the piston. The spring 234 directly contacts the cap 130 to hold the cap in place and bias the piston to expel fuel from the fuel chamber 240. The flange 17' allows a cavity 136 to be defined between the valve seat 116 and the cap 130, in which the moveable annular valve member 20 is located.

Extending radially inwardly from the flange 17' are a plurality of locating lands 150 which locate the valve member 20 centrally in the cavity while allowing for a significant flow area between the lands 150 around the periphery of the valve member 20. Such lands may also be present on the piston 10 shown in Figure 2. The piston 110 is provided with radially extending apertures 114 to allow for the escape of fuel vapour and to prevent trapping of such vapour below the valve seat 116.

The components described above are typically fabricated from stainless steel. However, they could be injection moulded in plastic. The components 116 and 20 described above in particular are suited to injection moulding.

Figures Ba -8d show the fuel injector of the present invention in use.

Figure Ba shows the fuel injector 219 in which the piston 10 is in its top stop position. The inlet check valve 11 as described in any of the embodiments above is closed, and there is no fluid flow in this position.

Figure 8b shows the fuel injector 219 with the solenoid coil 232 energised with an electric current. The piston 10 is drawn down by the magnetic flux flowing in the back-iron 233, towards the back-iron 233. The annular valve member 20 is forced upwardly by the fluid within the piston body 10.

The inlet check valve 11 opens allowing fluid to flow readily through the orifices 18, through and around the annular valve member 20, and through the orifices 34. The fluid flows into and replenishes the pumping chamber 240 as the piston 10 continues to move downwards.

Figure Bc shows the piston 10 pulled into engagement with the back-iron 233 whilst the solenoid 232 is energised.

The annular valve member 20 is still held up (i.e. the valve is open) by fluid continuing to enter the pumping chamber 240.

Figure 8d shows the solenoid de-energised. The piston moves upwardly driven by the spring 234. The upward movement of the piston 10 forces fluid out from the pumping chamber 240. During this movement the annular valve member is urged against the valve seat, and so the inlet valve 11 remains closed. Thus, all the fluid expelled from the pumping chamber 240 flows out through the one-way outlet check valve 238 and out of the fuel injector through the outlet 237.

When the piston 10 reaches its top stop the cycle will begin again from Figure Ba.

The solenoid has been described as drawing the piston back when energised, the spring causing motion of the piston to expel fuel when the solenoid is de-energised.

Alternatively, the spring may be configured to draw the piston back to allow re-filling of the fuel chamber, and the solenoid and back-iron configured to cause piston motion to expel fuel when the solenoid is energised.

Claims

-10 - CLAI MS

1. A fuel injector comprising: a housing in which a fuel chamber is formed; a piston which is slidable axially in a bore in the housing to draw fuel into and force fuel out of the fuel chamber; a fuel inlet; a fuel outlet; a one-way inlet valve which allows fuel to be drawn into the fuel chamber from the fuel inlet while preventing fuel being expelled from the fuel chamber to the fuel inlet; a one-way outlet valve which allows fuel to be expelled from the fuel chamber to the fuel outlet while preventing fuel being drawn back into the fuel chamber from the fuel outlet; wherein: the fuel inlet comprises a fuel inlet passage in the piston via which fuel is delivered into the fuel chamber; the one-way inlet valve is mounted in the piston to control flow of fuel from the fuel inlet passage in the piston to the fuel chamber; and the one-way inlet valve comprises: a valve seat having a plurality orifices arranged in an annular ring; and a moveable valve member engageable with the valve seat to close the apertures in the valve seat, the valve member being annular and having a central aperture through which fluid can flow when the valve is open.

-11 -

2. A fuel injector as claimed in claim 1 wherein the valve member is an annular disc.

3. A fuel injector according as claimed in claim 1 or claim 2 wherein each of the orifices in the valve seat is circular.

4. The fuel injector as claimed in any one of the preceding claims wherein when the one-way inlet valve is open then fuel flows both thorough the central aperture in the annular valve member and around a periphery of the annular valve member.

5. A fuel injector as claimed in any one of the preceding claims wherein the one-way inlet valve further comprises a cap having a plurality of orifices through which liquid can flow when the valve is open, the cap defining with the valve seat a cavity in which the annular valve member is located.

6. A fuel injector as claimed in claim 4 wherein the cap has a central orifice and a plurality of further orifices arranged in a annular ring around the central aperture, each of the orifices in the annular ring being aligned with the annular valve member such that when the valve member engages the cap then a portion of the annular valve member remains exposed in each orifice in the annular ring while still allowing fuel flow around a/the periphery of the annular valve member through the orifices.

-12 -

7. A fuel injector as claimed in claim 5 or claim 6 wherein each of the orifices in the cap are circular.

8. A fuel injector as claimed in any one of the preceding claims wherein the valve seat is formed as an integral part of the piston.

9. A fuel injector as claimed in any one of claims 1 to 7 wherein the valve seat is formed as a separate component and secured in place in the piston.

10. A fuel injector as claimed in claim 9 wherein the valve seat is secured in place by a spring which also biases the piston to expel fuel from the fuel chamber.

11. A fuel injector as claimed in any one of the preceding claims comprising: a spring biasing the piston to expel fuel from the fuel chamber, and a solenoid operable to draw back the piston to effect fuel flow into the fuel chamber.

12. A fuel injector as claimed in any one of the preceding claims comprising a plurality of locating lands around the valve seat which locate the valve member centrally on the valve seat while allowing for a flow area between the lands around the periphery of the valve member.

-13 -

13. A fuel injector substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

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