GB2452954A

GB2452954A - A fluid injector having a reed valve

Info

Publication number: GB2452954A
Application number: GB0718371A
Authority: GB
Inventors: Jeffrey Allen; Paul Bartholomew Ravenhill; 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: GB2452954B; GB0718371D0

Abstract

The fuel injector (19) comprises a reed valve (35) . The reed valve has at least one orifice and at least one reed valve blade, the or each reed valve blade having a valve head attached to at least one resilient spring arm. The or each valve head opens and closes a respective orifice in the valve seat. A support surrounds the reed valve blade(s). Each spring arm extends inwardly from the support and is curved.

Description

T

--245295

A REED VALVE FOR A FUEL INJECTION SYSTEM AND A FUEL

INJECTION SYSTEM HAVING SUCH A REED VALVE

The present invention relates to a reed valve for a fuel injection system and a fuel injection system having such a reed valve.

Most internal combustion engines in automobiles currently use fuel injection systems to supply fuel to the combustion chambers of the engine. Fuel injection systems have replaced the earlier technology of carburettors because they give more control of delivery of fuel and enable the engine to meet emission legislation targets as well as improving the overall efficiency of the engine.

Some fuel injectors in current use include a positive displacement pump and one or more one-way valves. A one-way valve may be located at a fuel outlet from the fuel injector, in order to allow fuel to be dispensed from the fuel injector and prevent fuel from returning into the fuel chamber. It is known to use a reed valve as a one-way valve. The reed valve may be a thin flexible strip which is secured at one end. The other end of the blade lies over a fuel outlet. Air pressure causes the strip to flex and open outwardly, allowing fuel to be dispensed. The reed valve blade closes again due to the resilience of the strip when the pressure decreases.

Known reed valves have the disadvantage that the selection of opening characteristics of the reed valve blades is restricted by the small size of the fuel injector.

The reed valve blade may therefore not open as quickly as desired and/or does not open as wide as desired.

The present invention provides, in a first aspect, a reed valve for a fuel injector comprising: a valve seat comprising at least one orifice; at least one reed valve blade, the or each reed valve blade having a valve head attached to at least one resilient spring arm, the or each valve head being operable to open and close a respective orifice in the valve seat; a support surrounding the or each reed valve blade, the or each spring arm extending inwardly from the support, and wherein the or each spring arm is curved..

The present invention provides, in a second aspect, 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 or 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 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 is a reed valve comprising:a valve seat comprising at least one orifice; at least one reed valve blade, the or each reed valve blade having a valve head attached to at least one resilient spring arm, the or each valve head being operable to open and close a respective orifice in the valve seat; a support surrounding the or each reed valve blade, the or each spring arm extending inwardly from the support, and wherein the or each spring arm is curved.

Thus, the reed valve can open quickly and/or fully to provide efficient dispensation of fuel from the fuel injector.

The present invention provides, in a third aspect, a reed valve for a fuel injector comprising: a valve seat comprising at least one orifice; at least one reed valve blade, the or each reed valve blade having a valve head attached to at least one resilient spring arm, the or each valve head being operable to open and close a respective orifice in the valve seat; a support surrounding the or each reed valve blade, the or each spring arm extending inwardly from the support, and wherein each spring arm connects a respective valve head to a point on the support spaced apart peripherally from a point of intersection of a straight line extending from the centre of the support through the centre of that valve head.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a fuel injector according to the present invention; Figure 2 is a front view of a first embodiment of a reed valve blade arrangement according to the present invention suitable for use in the fuel injector of Figure 1; Figure 3 is a perspective view of the reed valve blade arrangement of Figure 2; Figure 4 is a cut-away cross-section view of part of a fuel injector according to the present invention; Figure 5 is an end view of the part of the fuel injector of Figure 3; Figure 6 is a side view of a cap forming part of the present invention with the body of Figure 4; Figure 7 is an end view of the cap of Figure 6; Figure Ba is a front view of a second embodiment of a reed valve blade arrangement according to the present invention; Figure 8b is a perspective view of the reed valve blade arrangement of Figure Ba; Figure 9a is a front view of a third embodiment of a reed valve blade arrangement according to the present invention; Figure 9b is a perspective view of the reed valve blade arrangement of Figure 9a; Figure lOa is a front view of a fourth embodiment of a reed valve blade arrangement according to the present invention; Figure lOb is a perspective view of the reed valve blade arrangement of Figure lOa; Figure ha is a front view of a fifth embodiment of a reed valve blade arrangement according to the present invention; Figure llb is a perspective view of the reed valve blade arrangement of Figure ha.

Figures 12a to 12d are schematic illustrations of the fuel injector of Figure 1 according to the present invention in different stages during use.

S The present invention relates to a reed valve for a fuel injector and a fuel injector having such a reed 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 19 with a piston body 30 located in a pumping chamber, or fuel chamber, 36. A fuel inlet 42 provides for fuel to enter the fuel injector 19 and flow into a fuel passage passing through the piston body 30.

A fuel inlet check valve 35 is situated in the fuel passage.

The fuel inlet check valve 35 is a one-way valve. The fuel inlet check valve 35 can allow the flow of fuel from the piston body 30 to the pumping chamber 36.

A solenoid 32 is provided with a back-iron 33 for pulling the piston body 30 downwardly as shown when energised. A piston spring 34 pushes the piston 30 away from the back-iron 33 when the solenoid is de-energised, in order to expel fuel from the pumping chamber 36.

Fuel is dispensed from the pumping chamber 36 to a fuel outlet 37 via a one-way outlet check valve 38. The operation of the fuel injector 19 will be described further with reference to Figures 12a -12d.

Figures 2 to lib show in detail the one-way inlet valve of the fuel injector, the one-way inlet valve being a reed valve as illustrated.

Figures 2 and 3 show a blade assembly 60 which forms part of the reed valve. The blade assembly GO comprises three independent reed valve blades 61. Each of the reed valve blades 61 has a valve head 62 and a spring arm 64 extending from the valve head 62. The three reed valve blades 61 all extend from a surrounding annular rim 66. The reed valve blades are each shaped like a comma, with a circular sealing surface provided by each valve head and a curved spring arm extending from the sealing surface in a swirl-like manner. The swirl shape is needed to achieve the desired length of spring arm (a certain length is needed to ensure that the arm does not overstretch) The reed valve blade assembly 60 is formed from a thin plate. The reed valve blade assembly 60 is formed of an elastically deformable material, e.g. metal, in particular stainless steel. At rest, the three reed valve blades 61 and rim 66 lie in the same plane. At rest, the valve heads 62 and arms 64 of each reed valve 61 also extend in the same plane.

The valve head 62 and arms 64 of each reed valve 61 are integrally formed. The rim 66 is preferably integrally formed with the arms 64 of each reed valve blade 61.

The arm 64 of each reed valve blade 61 extends from an inner surface of the annular rim 66. The three arms 64 are equally spaced around the circumference of the rim 66.

The arms 64 are curved in the plane (at rest) of the valve heads 62. The arms 64 extend adjacent to the rim 66.

Each arm 64 subtends an angle of approximately 900 of the circumference of the rim.

Each valve head 62 is substantially disc-shaped. Each valve head 62 has a diameter larger than the width of the arm 64 to which it is attached. Each valve head 62 extend radially inwardly of a respective arm 64, i.e. the arms 64 are connected to the valve heads 66 at a radially outward part on the valve head 62. Each valve head 62 and attached arm 64 together form a comma-shaped reed valve element.

Each of the reed valve blades 61 is independently operable. The opening and closing characteristics of the reed valve will depend on the resilience of the arms 64.

The curvature of the arms 64 means that the arms 64 have a long length relative to the overall size of the reed valve blade assembly 60. The curvature of the arms 64 allows them to be located substantially parallel and alongside the annular rim 62. This allows three valve heads to be packaged within a small overall area, each having a relatively long arm 64 to provide a good opening characteristics.

The rim 66 is provided with an alignment protrusion 68 extending radially outwardly. The alignment protrusion 68 can engage in a notch to ensure that the reed valve blade assembly 60 is properly orientated. The alignment protrusion 68 also inhibits rotation of the reed valve blade assembly 60 during use.

Figures 4 and 5 show a piston body 70 forming the piston of the injector of Figure 1. The piston body 70 has a bore 72 which receives fuel from inlet port 74. The piston is arranged to dispense fuel through the three outlet orifices 76. The outlet orifices 76 open onto a stepped recess forming a valve seat 78 and a cap seat 80. The reed valve blade assembly 60 shown in Figures 2 and 3 is received on the valve seat 78. The alignment protrusion 68 is received in the alignment recess 79. The valve heads 62 are aligned one each with the orifices 76. A cap, as will be described with reference to Figures 8 and 9 is received in the cap seat 80 to secure the reed valve blade assembly 60 in place.

Figures 6 and 7 show a cap 84 for attaching to the piston body 70 to keep the reed valve blade assembly 60 in position. The cap 84 is formed of a plate 86 having three apertures 88. The apertures 88 are aligned with the orifices 76 in the piston body 70, and with the valve heads 62. The apertures 88 have a diameter larger than the valve head 62. The plate 86 is provided with an annular flange 90. The annular flange 90 contacts the rim 66 of the reed valve blade assembly 60, and is located in the valve seat 78. The cap 84 as well as holding the reed valve blade assembly 60 in place also prevents the spring arms overstretching. The reed valve blade assembly 60 is sandwiched between the valve seat and the cap 84.

Alternatively, the cap 84 may be an annular ring defining a single aperture, extending around the periphery of the valve blade assembly. Fluid flowing from each of the outlet orifices 76 would pass through the single aperture.

The cap 84 would still retain the reed valve blade assembly in place, and would not limit movement of the reed valve heads.

Figures 8a to lib show alternate reed valve blade assemblies, which can be used in place of the blade assembly described above. The location and number of outlet orifices 76 and apertures 88 in the cap 84 may be varied accordingly to ensure that the or each valve blade head is operable to open and close a respective orifice in the valve seat. The location and size of the or each aperture 88 in the cap 84 may need to be varied to ensure fuel flow through the reed valve when the or each orifice is open.

Figures 8a and 8b show a blade assembly 160 comprising three independent reed valve blades. Each of the reed valve blades 161 has a valve head 162 and a resilient curved spring arm 164. The blade assembly 160 has an annular rim 166 surrounding the reed valve blades 161, the three reed valve blades 161 extending inwardly from the rim 166.

-10 -The reed valve blades 161 are substantially shaped like a comma, having a circular head 12 and a curved tail. The spring arm 164 joins the head 162 substantially centrally on the valve head, with respect to the longitudinal direction of the spring arm 164. This contrasts with the valve blades 61 shown in Figures 2 and 3, in which the arm 64 is connected to the valve head 66 at a radially outward part, i.e. to one side of the valve head 66 following the longitudinal length of the arm 64.

Figures 9a and 9b show a third embodiment of a blade assembly 260. The blade assembly comprises three independent reed valve blades 261 each having a circular valve head 262 and a resilient curved spring arm 264. The blade assembly 260 has an annular rim surround the three reed valve blades 261 from which the curved spring arms 264 extend inwardly. The curved arms are longer than in the other described embodiments. The spring arms 264 subtend an angle of approximately 180° to partially encircle the heads 262. The spring arms 264 are joined to the heads 262 at a point substantially diametrically opposite to the point where the rim 266 joins the spring arms 264. The reed valve blades 261 are arranged to extend substantially circurnferentially inside the rim 266, which allows packaging of the three blades 261 within the rim 266.

The proportionately long spring arms 264 provide a lower spring rate to control opening of the heads 262.

Figures l0a and lob show a fourth embodiment of reed valve blade assembly 360. The blade assembly 360 comprises a single reed valve blade 361 having a valve head 362. The -11 -valve head 362 is supported by two resilient curved spring arms 364. Each of the curved spring arms 364 is joined to an annular rim 366 which surrounds the valve blade 361.

Each of the spring arms 364 lies alongside and partially encircles the head 362, each spring arm 364 subteriding an angle of approximately 1500. The spring arms 364 extend on opposite sides of the circular head 361.

The presence of two spring arms for a single head means that the head 362 lifts straight up from a valve seat, and remains in a plane perpendicular to the longitudinal axis of an orifice defined by the valve seat. This contrasts with the embodiments having a single arm per head, in which resilient bending of the curved arm means that the valve head is lifted at an angle to the valve seat.

Figures lla and lib show a fifth embodiment of a reed valve assembly 460. The blade assembly 460 comprises three independent reed valve blades 461. Each of the reed valve blades 461 has a valve head 462 and a resilient straight spring arm 464. The blade assembly 460 has an annular rim 466 surrounding the reed valve blades 461, the three reed valve blades 461 extending inwardly from the rim 466.

Each spring arm 464 joins the respective valve head 462 substantially centrally on the valve head, with respect to the longitudinal direction of the spring arm 464.

Each spring arm 464 connects a respective valve head 462 to a point on the rim spaced apart circumferentially -12 -from a point of intersection of a radius of the assembly passing from the centre of that valve head.

During operation as the piston 30 moves to draw fuel into the fuel chamber the spring arms of the valve blades allow the valve heads to move out of engagement with the valve seat to open the orifices in the valve seat and allow fuel flow. Then when the piston comes to a stop the elasticity in the spring arms returns the valve heads into engagement with the valve seat to close the orifices. During movement of the piston to expel fuel from the fuel chamber both the elasticity of the spring arms and also the pressure differential across the valve will keep the valve heads in firm engagement with the valve seat and the orifices in the valve seat remain closed. The cycle will then begin again.

Testing has shown that the reed valve described above performs better than the known disc valve. Partly this is because it closes automatically under the spring force in a no flow situation. It achieves a higher operating speed and a better efficiency. The valve improves flow area and gives a smoother flow path (the fluid does not have flow right around the periphery of a disc) ;this more than makes up for the initial resistance to opening occasioned by the spring force. The valve in any event improves expulsion of fuel from the chamber by shutting quicker. The reed valve is easy to manufacture.

Figures l2a to 12d show the fuel injector in use. The fuel injector may include the reed valves of any of the described embodiments.

-13 -Figure 12a shows the fuel injector 19 in which the piston 30 is in its top stop position. The inlet reed check valve 35 is closed, and there is no fluid flow in this position.

Figure 12b shows the fuel injector 19 with the solenoid coil 32 is energised with an electric current. The piston 30 is drawn down by the magnetic flux flowing in the back-iron 33, towards the back-iron 33. The reed valve blades 61 in the check valve 35 are forced upwardly by the fluid within the piston body 30. The inlet check valve 35 opens allowing fluid to flow readily through the orifices 76, around the reed valve blades, and through the orifice(s) 88. The fluid flows into and replenishes the pumping chamber 36 as the piston 30 continues to move downwards.

Figure 12c shows the piston 30 pulled into engagement with the back-iron 33 whilst the solenoid 32 is energised.

The reed valve blades 61 are still held up (i.e. the valve 35 is open) by fluid continuing to enter the pumping chamber 36.

Figure l2d shows the solenoid de-energised. The piston moves upwardly driven by the spring 34. The upward movement of the piston 30 forces fluid out from the pumping chamber 36. During this movement the reed valve blades 61 are urged against the valve seat 78, and so the inlet valve remains closed. Thus, all the fluid expelled from the pumping chamber 36 flows out through the one-way outlet check valve 38 and out of the fuel injector through the outlet 37.

-14 -When the piston 30 reaches its top stop the cycle will begin again from Figure l2a.

In use, it has been found that it is the resilience of the spring arms which closes the valve rather than the pressure differential across the valve.

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, and the solenoid configured to cause piston motion to expel fuel when the solenoid is energised.

The reed valve has been described as located on a piston of a fuel injector. Alternatively, the reed valve described may be used with a fuel injection system different to that described above, or the reed valve may be used as a one-way valve in any type of system.

The rim surrounding the or each valve blade has been described as annular. Alternatively, the rim may form an ellipse, square, or other regular or non-regular shape.

The valve heads in the above embodiments have been described as substantially circular. Alternatively, the valve heads may be triangular in shape. In one embodiment, three triangular heads may be provided. Each triangular head defines a sector covering just under a third of a circle, and located within an annular rim. A curved arm joins each head to the rim, each curved arm extending substantially circumferentially around the radially outer -15 -edge of each head. The apertures in the valve seat may also be triangular in this embodiment. Alternatively, any of the apertures described may be non-circular, i.e. square, rectangular.

In each of the above embodiments the curved arm extends both circumferentially and radially to connect the or each valve head to the rim. For an annular support, the or each spring arm connects a respective valve head to a point on the annular support spaced from a point of intersection with the annular support of a radius passing from the centre of the annulus through a centre of the said valve head. In other words, applicable to a non-circular rim or support, each spring arm connects a respective valve head to a point on the rim spaced apart peripherally from a point of intersection of a line extending from the centre of the rim through the centre of that valve head. This provides for good packaging of one or more valve heads within a certain overall area.

The spring arm in some embodiments extends inwardly from the support into proximity with the valve head, and extends proximal to and spaced apart from the valve head around part of the circumference of the valve head before joining with the valve head. Preferably, the spring arm is proximal to and spaced apart from the valve head for substantially half of the circumference of the valve head.

In an alternate embodiment, reed valve blades are arranged on a conical or frustro-conical end surface of a piston, such that the blades are angled radially outwardly.

This allows improved opening of the blades. Alternatively, -16 -the reed valve assembly of any of the above described embodiments may be located at the end of an inwardly tapered channel. The tapering of the channel increases the pressure, improving the opening of the blades.

The valve seat of any of the embodiments may be provided with a flange around each the orifices 76. The reed valve head(s) contact the respective flange, and so are spaced apart from the remainder of the valve seat when closed. This may improve sealing of the reed valve heads against the valve seat.

The reed valves of any of the embodiments may be formed with a deformation out of the plane of the rim, such that at rest they are biased against the valve seat. Such reed valves would therefore have a pre- loaded against the opening forces. This would also counter plastic deformation of the reed valves during use, which tends to bend the reed valves upwardly, i.e. away from the valve seat.

In an alternate embodiment, the cap or securing ring may be integrally formed with the piston body, and the valve seat formed as a separate component. The valve seat may be secured in place by the spring which also actuates movement of the piston to expel fuel.

Where in this specification, including the claims,

reference is made to comma-shaped' this does not require the valve head to be circular in shape and must be read as permitting the valve head to have any shape. The term comma-shaped is used to denote a shape comprising a head portion extending from which is a curved tail.

-17 -The reed valve assembly has been described as having three reed valves. Alternatively, four reed valves may be located within each support.

Any feature of any embodiment may be used with or present in any other embodiment.

Claims

U -18 - CLA I MS

1. A reed valve for a fuel injector comprising: a valve seat comprising at least one orifice; at least one reed valve blade, the or each reed valve blade having a valve head attached to at least one resilient spring arm, the or each valve head being operable to open and close a respective orifice in the valve seat; a support surrounding the or each reed valve blade, the or each spring arm extending inwardly from the support, and wherein the or each spring arm is curved.

2. A reed valve blade as claimed in claim 1 wherein each reed valve blade is comma shaped with each spring arm forming a curved tail of the comma-shaped reed valve blade.

3. A reed valve as claimed in claim 1 or claim 2 wherein the or each reed valve blades extend inwardly from the support, and each spring arm connects a respective valve head to a point on the support spaced apart peripherally from a point of intersection of a straight line extending from the centre of the support through the centre of that valve head.

4. A reed valve as claimed in any one of the preceding claims wherein the or each of the spring arms is integrally formed with the annular support.

5. A reed valve as claimed in any one the preceding claims wherein each valve head and spring arm are integrally formed.

-19 -

6. A reed valve as claimed in any one of the preceding claims wherein the or each spring arm is curved through an angle of approximately 300, 90°, 110° or 150°.

7. A reed valve as claimed in any one of the preceding claims wherein the or each curved arm has a length greater than a largest dimension of the valve head.

8. A reed valve as claimed in any one of the preceding claims wherein the or each curved arm has a width smaller than both the width and the length of the valve head when the valve head is non-circular or smaller than the diameter of the valve head when the valve head is circular.

9. A reed valve as claimed in any one of the preceding claims wherein each spring arm has a width substantially uniform along the length of the spring arm.

10. A reed valve as claimed in any one of the preceding claims wherein each of the valve heads when at rest lies in a common plane.

11. A reed valve as claimed in any one of the preceding claims wherein the or each valve head is substantially circular or substantially triangular.

12. A reed valve as claimed in any one of the preceding claims wherein the reed valve comprises three reed valve blades, each reed valve blade having one valve head and one curved spring arm.

-20 -

13. A reed valve as claimed in any one of the preceding claims wherein the reed valve comprises one reed valve blade having one valve head supported by two curved spring arms.

14. A reed valve as claimed in any one of the preceding claims wherein the spring arm extends inwardly from the support into proximity with the valve head, and extends proximal to and spaced apart from the valve head around part of the circumference of the valve head before joining with the valve head.

15. A reed valve as claimed in claim 14 wherein the spring arm is proximal to and spaced apart from the valve head for substantially half of the circumference of the valve head.

16. A reed valve as claimed in any one of the preceding claims wherein the valve seat is arranged on a conical or frusto-conical surface such that the or each reed valve blade opens in a substantially radial direction.

17. 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 or 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; ( -21 -a one-way outlet valve which allows fuel to be expelled from the fuel chamber to the fuel outlet while preventing fuel being drawn 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 is a reed valve comprising: a valve seat comprising at least one orifice; at least one reed valve blade, the or each reed valve blade having a valve head attached to at least one resilient spring arm, the or each valve head being operable to open and close a respective orifice in the valve seat; a support surrounding the or each reed valve blade, the or each spring arm extending inwardly from the support, and wherein the or each spring arm is curved.

18. A fuel injector as claimed in claim 17 wherein the reed valve is as claimed in any one of claims 2 to 16.

19. A reed valve for a fuel injector comprising: a valve seat comprising at least one orifice; at least one reed valve blade, the or each reed valve blade having a valve head attached to at least one resilient spring arm, the or each valve head being operable to open and close a respective orifice in the valve seat; a support surrounding the or each reed valve blade, the or each spring arm extending inwardly from the support, and wherein each spring arm connects a respective valve head to a point on the support spaced apart peripherally -22 -from a point of intersection of a straight line extending from the centre of the support through the centre of that valve head.

20. A reed valve as claimed in claim 19 wherein the support is annular and the or each reed valve blades extend inwardly from the support, and each spring arm connects a respective valve head to a point on the annular support spaced from a point of intersection with the annular support of a radius passing from the centre of the annulus through a centre of the said valve head.

21. A reed valve as claimed in claim 19 or 20 wherein the spring arm is straight or is curved.

22. 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 or 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 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; -23 -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 is a reed valve comprising: a valve seat comprising at least one orifice; at least one reed valve blade, the or each reed valve blade having a valve head attached to at least one resilient spring arm, the or each valve head being operable to open and close a respective orifice in the valve seat; a support surrounding the or each reed valve blade, and wherein each spring arm connects a respective valve head to a point on the support spaced apart peripherally from a point of intersection of a straight line extending from the centre of the support through the centre of that valve head.

23. A fuel injector substantially as hereinbefore described with reference to and as shown in any one of the accompanying drawings. 2 0