Fuel injector

Abstract

A fuel injector (10) for an internal combustion engine, the fuel injector comprising a fuel injector inlet (30), a fuel injector outlet and a housing (18, 26; 18, 318, 348); a fuel supply passage (32) defined within the housing (18, 26; 18, 318, 348) between the fuel injector inlet (30) and the fuel injector outlet and comprising an upstream fuel passage portion (140; 240; 340; 440) and a downstream fuel passage portion (142; 242; 342; 442). The upstream fuel passage portion defines an upstream axis (B-B) aligned with the direction of fuel flow through the upstream fuel passage portion and the downstream fuel passage portion defining a downstream axis (C-C) aligned with the direction of fuel flow through the downstream fuel passage portion. A branch passage (34) comprising an inlet (44) which opens into the fuel supply passage so that a first proportion of fuel flow through the upstream fuel passage portion flows into the branch passage (34), the branch passage (34) defining a branch axis (D-D). A separation surface (146; 246; 346; 446) defined within the fuel supply passage spaces the inlet (44) from the upstream fuel passage portion (140; 240; 340; 440) such that a proportion of the flow through the upstream fuel passage portion deflects away from the upstream axis (B-B), past the separation surface (146; 246; 326; 446), before the first proportion of the flow enters the inlet (44) and a second proportion of the flow flows downstream to the downstream fuel passage portion (142; 242; 342; 442).

Description

[0001] FUEL INJECTOR

[0002] FIELD OF THE INVENTION

[0003] This invention relates to a fuel injector and, in particular, to a fuel injector for supplying fuel to internal combustion engine.

[0004] BACKGROUND

[0005] The control valves and flow restrictions used in diesel and gasoline fuel injectors often require flow passages down to the size of tens of micrometers. This makes them highly susceptible to becoming blocked by particles of debris which may be introduced into the injector. If flow passages become blocked in any way, injector performance is compromised and the injector can fall outside of the required performance specification. Particles which become entrenched in the fuel can also cause damage to the valve sealing surfaces which lead to accelerated wear, resulting in leakage and / or performance change.

[0006] It is known to provide specific filter components within a fuel injector to help counteract this problem. However, these components sometimes are not able to stop the smallest of foreign particles and sometimes debris that originates within the injector itself may avoid the filter location. An edge filter or a laser-drilled filter may be incorporated within an injector to offer the greatest protection. However, these components do require space within the injector which is an inconvenience and / or risk of structural failure due to elevated stress. Such filters also restrict the fuel flow, reducing the pressure available at the nozzle spray holes.

[0007] It is against this background that the invention has been devised.

[0008] SUMMARY OF THE INVENTION

[0009] According to the invention, there is provided a fuel injector for an internal combustion engine, the fuel injector comprising a fuel injector inlet, a fuel injector outlet and a housing. A fuel supply passage is defined within the housing between the fuel injector inlet and the fuel injector outlet. The fuel supply passage comprises an upstream fuel passage portion and a downstream fuel passage portion, the upstream fuel passage portion defining an upstream axis aligned with the direction of fuel flow through the upstream fuel passage portion and the downstream fuel passage portion defining a downstream axis aligned with the direction of fuel flow through the downstream fuel passage portion. The injector comprises a branch passage comprising an inlet opening which opens into the fuel supply passage so that a first proportion of fuel flow through the upstream fuel passage portion flows into the branch passage. A separation surface is defined within the main fuel flow passage which spaces the inlet opening from the upstream fuel passage portion such that a proportion of the flow through the upstream fuel passage portion deflects away from the upstream axis, past the separation surface, before the first proportion of the flow enters the inlet and a second proportion of the flow flows downstream to the downstream fuel passage portion.

[0010] The branch passage defines a branch passage axis aligned with the direction of fuel flow through the branch passage.

[0011] In embodiments of the invention, the upstream axis may be displaced laterally relative to the downstream axis, along the branch axis, to define the separation surface. The separation surface typically defines a maximum overlap dimension which is between 10-15% of the diameter of the downstream fuel passage portion.

[0012] In embodiments of the invention, the maximum overlap dimension defines an overlap cross sectional area which is no more than 30% of the cross sectional flow area of the downstream fuel passage portion. This ensures that the flow restriction which results from the overlap does not affect the flow rate through the flow passage detrimentally.

[0013] The upstream axis may be displaced laterally relative to the downstream axis so that the upstream axis is displaced further (measured along the branch axis) from the inlet than the downstream axis.

[0014] In embodiments of the invention, the main housing may comprise an upstream housing part within which the upstream fuel passage portion is defined, at least in part, and a downstream housing part within which the downstream fuel passage potion is defined, at least in part. The separation surface may be defined at an interface between the upstream and downstream housing parts. For example, the separation surface may be defined by a lower surface of the upstream housing part.

[0015] In other examples, the separation surface may be defined within the upstream housing part.

[0016] In embodiments, the upstream axis and the downstream axis may be parallel with one another.

[0017] Alternatively, the upstream axis may be inclined relative to the downstream axis.

[0018] The fuel injector may further comprise a control valve for the valve needle, wherein the branch passage is configured to deliver fuel from the main fuel supply passage to the control valve.

[0019] Instead of the upstream and downstream axes being offset laterally relative to one another, the upstream axis and the downstream axis may be coaxial. The upstream fuel passage portion may have a different diameter to the downstream fuel passage portion.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order that the invention may be more readily understood, preferred non-limiting embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0022] Figure 1 is a cross section of a fuel injector of the prior art in which a problem may arise due to debris introduced to or generated within the injector;

[0023] Figure 2 is a cross section of an alternative fuel injector of the prior art;

[0024] Figures 3 and 4 show two different examples of a cross section of an injector to illustrate how upstream and downstream fuel passages within the injector are typically configured;

[0025] Figure 5 is a cross section, similar to Figures 3 and 4, but in which a manufacturing variation leads to an ‘underlap’ between the upstream and downstream fuel passages; and

[0026] Figure 6 shows a cross section view of an embodiment of the invention in which an overlap region is defined between the upstream and downstream fuel passages;

[0027] Figure 7 is a top cross section view, along a section perpendicular to that shown in Figure 6, to show the overlap region more clearly; and

[0028] Figures 8 to 11 are cross section views of alternative embodiments of the invention.

[0029] In the drawings, as well as in the following description, like features are assigned like reference signs.

[0030] Throughout this description, terms such as ‘upper’ and ‘lower’, and other directional references, are used with reference to the orientation of the fuel injector as shown in the accompanying drawings. However, it will be appreciated that such references are not limiting and that fuel injectors according to the invention can be used in any orientation.

[0031] DETAILED DESCRIPTION OF THE INVENTION

[0032] Referring to Figure 1 , there is shown a fuel injector 10, or injector assembly, for injecting fuel in an internal combustion engine. The injector 10 is of the type in which an actuator 12 controls a control valve 14 which in turn controls the movement of an injector valve needle 16. The control valve 14 includes a valve member (not labelled) which is moveable within a valve housing 18, towards and away from a valve seat, to control fuel pressure in a control chamber (not visible in Figure 1). In dependence on the fuel pressure in the control chamber, the injector valve needle 16 is engageable with a valve needle seat area 20 to control the delivery of fuel between an injector delivery chamber 22 and a combustion chamber 24. A spring 27 is provided to urge the valve needle 16 against the valve needle seat area 20 to prevent injection. The valve needle 16 extends into a injector housing part in the form of a needle guide housing 26 arranged immediately beneath the valve housing 18.

[0033] Referring also to Figure 2, a lift plate 28 is defined between the facing surfaces of the valve housing 18 and the needle guide housing 26. The lift plate 28 defines a part of a main fuel supply passage 32 through the injector. The injector 10 also includes an inlet 30 for receiving high pressure fuel. The inlet 30 communicates with the main fuel supply passage 32 from where fuel is delivered to the injector delivery chamber 22. This fuel supply passage 32 may be considered to be the main fuel supply passage through the injector 10. The main fuel supply passage 32 has a branch passage 34 which delivers fuel to the control valve 14 (the branch passage is not visible in the cross section of Figure 1). The branch passage 34 communicates with a valve chamber 36 defined by a bore in the valve housing 18. When the control valve 14 is moved away from the valve seat, fuel is able to flow past the valve seat and into the control chamber. In this way valve needle movement is controlled to control injection. The details of how movement of the valve needle is controlled by the control valve will be familiar to a person skilled in the art and will not be described in further detail here. Figure 2 is an alternative prior art fuel injector in which the configuration of the fuel supply passage 32 through the injector housings is slightly different, but again in which a branch passage 34 extends from the main fuel supply passage 32. An interface is defined directly with the needle guide housing 26 and the lift plate 28 of Figure 1 is removed.

[0034] The invention concerns the configuration of the main fuel supply passage 32 and the branch passage 34 and how a proportion of the flow through the main fuel supply passage 32 deviates or deflects through the branch passage 34 and a proportion flows onward to the downstream parts of the injector 10. In particular, the invention concerns how unwanted particles within the flow can be preferentially directed through the main flow. Rather than being directed through the more sensitive parts of the injector around the control valve.

[0035] By way of background to the invention, Figures 3 and 4 show a configuration of passages in a known fuel injector where the presence of debris may be a problem. Referring to Figure 3, the injector comprises upper and lower housing parts, such as the valve housing 18 and the needle guide housing 26 in Figure 1 (in this case the lift plate of Figure 1 is removed between the parts 18, 26). In an alternative arrangement (not shown), the upper and lower housing parts of Figure 3 may represent the valve housing 18 and the lift plate 28 of Figure 1 .

[0036] In Figure 3, the housing parts are labelled as 18 (valve housing) and 26 (needle guide housing). The housing parts 18, 26 have an interface 29, where facing surfaces of the housing parts 18, 26 engage one another. The housing parts 18, 26 are provided with respective upstream and downstream fuel passage portions 40, 42 which together define the main fuel supply passage 32 through the injector to deliver fuel to the valve needle seat area 20. The main fuel supply passage 32 therefore extends through both the upper and lower housing parts 18, 26 and traverses the interface 28 between the two parts 18, 26.

[0037] The upstream and downstream fuel passage portions 40, 42 are coaxially aligned with one another along an axis which defines the main axis A-A of the main fuel supply passage 40, 42. The axis of the upstream fuel passage portion 40 is identified as B-B and the axis of the downstream fuel passage portion 42 is identified as C-C, in this case the axes B-B and C-C being coaxial. The axis B-B represents the flow axis of fuel flowing through the upstream fuel passage portion 40 and the axis C-C represents the flow axis of fuel flowing through the downstream fuel passage portion 42. A branch passage 34 communicates with the main fuel supply passage (equivalent to the branch passage in Figure 1). The branch passage 34 is defined by a groove in the upper surface of the lower housing part 26 and has an inlet 44 and an outlet 45. The inlet 44 communicates with a region of the downstream fuel passage portion 42.

[0038] Figure 4 shows a similar configuration to that shown in Figure 3, except that the axis B-B of the upstream fuel passage portion 40 in the upper housing part 18 is angled relative to the axis C-C of the downstream fuel passage portion 42 in the lower housing part 26, rather than these axes being coaxial. In circumstances where it is necessary to angle the upstream fuel passage portion 40 relative to the downstream fuel passage portion, the conventional practice is to align the axes B- B, C-C of the passages at the interface 28, as shown in Figure 4.

[0039] One problem with the configuration of passages shown in Figures 3 and 4 is that, when manufacturing and assembly variations are considered, it is possible that a diameter ‘underlap’ is formed with the branch passage 34 at the interface 29, as shown in Figure 5. The diameter underlap II with the branch passage is defined as follows. In the cross-section of Figure 5, an internal wall of the upstream fuel passage portion 40 defines an outer surface S40 which is parallel to the axis B-B and an internal wall of the downstream fuel passage portion 42 defines an outer surface S42 which is parallel to the axis C-C. In the aligned configuration of Figure 3, these surfaces S40, S42 would be aligned but in the example in Figure 5 the surfaces S40.S42 are separated in a lateral direction relative to the axes, B-B and C-C, to define the diameter underlap II. As a consequence of this diameter underlap II the upstream fuel passage portion 40 communicates with the branch passage 34 not merely via what should be the defined inlet 44, but directly with the branch passage 34 along its axial length. An exposed surface 46 of the housing 26 is therefore presented to the incoming fuel flow through the upstream fuel passage portion 40. The presence of a diameter underlap II increases the risk of debris particles being entrained within the flow through the branch passage 34 to the valve chamber. Larger particles (and especially those with a higher Stokes number which readily detach from the fluid movement, typically having a size >100pm), may impact the exposed surface 46 in the region of the diameter underlap II and are therefore prevented from continuing with the main flow through the downstream fuel passage portion 42. The particles therefore become entrained within the branch flow 34 which is not desirable. The exposed surface 46 is defined by a surface of the lower housing part 26 and faces the incoming flow through the upstream fuel passage portion 40. Smaller particles (typically having a size of <100 pm) which track the fluid movement more closely also have a greater chance of entering the branch passage 34. The diameter underlap II effectively creates a region of stagnant flow near the inlet 44 to the branch passage 34, reducing the momentum of the particles in this region and increasing the volume of fuel from within which the flow through the branch passage 34 is taken. This increases the likelihood of the branch flow 34 containing these smaller particles.

[0040] It will be appreciated that the presence of a diameter underlap II corresponds to an area underlap also, but this is not represented on the two-dimensional crosssection figures.

[0041] Referring initially to Figures 6 and 7, in the present invention the problem of smaller particles entering the branch passage 34 is avoided by ensuring that a diameter overlap O is maintained between the upstream fuel passage portion 140 and the downstream fuel passage portion 142, as opposed to a diameter underlap II as in the prior art example. In the arrangement of Figures 6 and 7, the branch passage 34 has an inlet 44 which communicates with or opens into a portion of the downstream fuel passage portion 142 immediately beneath or downstream of the interface 29. In this embodiment the upstream fuel passage portion 140 has an axis B-B (referred to as the upstream axis) and the downstream fuel passage portion 142 has an axis C-C (referred to as the downstream axis), where the upstream axis B-B is displaced laterally, relative to the downstream axis C-C, by an overlap amount N. The displacement of the upstream axis B-B relative to the downstream axis C-C is in a direction away from the branch passage 34 so that the axis B-B is spaced further from the inlet 44 than the axis C-C, as best seen in Figure 6. In other words, the internal surface S140 of the upstream fuel passage portion 140 closest to the inlet 44 is displaced further from the inlet 44 than the internal surface S142 of the downstream fuel passage portion 142 closest to the inlet 44. A point of intersection between the upstream axis B-B and a branch axis D-D is displaced further from the inlet 44 than a point of intersection between the downstream axis C-C and the branch axis D-D, measured along the branch axis. The lateral displacement of the upstream axis B-B relative to the downstream axis C-C (i.e. measured in a direction perpendicular to the longitudinal axis of the upstream fuel passage portion 140, along D-D) defines a diameter overlap, indicated as O. The overlap O can be seen most clearly in Figure 7. The diameter overlap O results in an exposed surface 146 being defined by a lower surface of the upper housing 18 at the inlet 44 to the branch passage 34 and at the interface 29 between the two housings 18, 26. The exposed surface 146 does not face the incoming flow through the upstream fuel passage portion 140 but instead defines a separation surface for the fuel flow through the main flow passage. The separation surface 146 faces the downstream fuel passage portion 142.

[0042] The extent of the diameter overlap O is selected to ensure that no diameter underlap which may arise (as illustrated in Figure 5, for example) due to manufacturing variations negates the diameter overlap O entirely, and always leaves some lateral displacement of the downstream axis C-C relative to the upstream axis B-B. However, the extent of the diameter overlap O cannot be too large that excessive flow restriction may occur, between the upstream and downstream fuel passage portions 140, 142, which could reduce the fuel pressure transmitted to the injector outlet. By way of example, the manufacturing variation of axis position and bore diameter can result in a diameter underlap II of between 5-10% (corresponding to approximately 10-20% area underlap). The nominal overlap of the invention should ensure that there is a 5% diameter overlap in the worst case for manufacturing variation. To ensure this, a nominal 10-15% maximum diameter overlap O may therefore be typical in the invention (corresponding to 20-25% area overlap). The maximum diameter overlap (also referred to as the maximum overlap dimension) is measured along the branch axis D-D, as shown in Figure 7, and is the linear measurement of the maximum extent of the overlap between the upstream and downstream flow passage portions 140, 142.

[0043] A corresponding area overlap of greater than 30% (corresponding to a maximum overlap diameter of greater than around 18-20%) should be avoided as this may create an undesirable loss of fuel pressure when traversing the intersection due to the restricted flow area which results from an overlap of this significance. The diameter overlap percentage refers to the ratio of the distance of the maximum overlap dimension O (as indicated in Figure 7) relative to the diameter of the downstream fuel passage portion 142 (which in this case is the same as the diameter of the upstream fuel passage portion 140).

[0044] The maximum allowable area overlap percentage refers to the ratio of the surface area of the overlap (for example, the shaded area A in Figure 7) to the cross section of the smaller of the upstream fuel passage portion 140 and the downstream fuel passage portion 142. This is because the smallest cross section determines the overall pressure restriction or flow capacity.

[0045] The relative offset between the axes B-B, C-C to provide the diameter overlap O (and corresponding area overlap) ensures that particles of sufficient size to cause damage or blockage to the valve, or associated restrictions, are directed along the main flow passage (i.e. onward through the downstream fuel passage portion 142) rather than into the branch passage 34. The diameter overlap O creates a small region of flow separation at the inlet 44 of the branch passage 34, resulting in particles with a sufficiently high Stokes number being unable to follow the sharply turning fluid past the separation surface 146 towards the branch passage 34. Instead these particles detach from the flow to follow the main flow through the downstream fuel passage portion 142 and towards the injector outlet. The high sharpness of the corner creating the separation at the separation surface 146 means that even the smallest particles of concern are kept away from the flow through the branch passage 34. Even smaller particles may be able to flow around the separation region and enter the branch flow, but these can pass through the restrictions and the valve without causing problems.

[0046] It will be appreciated that the displacement of the upstream axis B-B from the downstream axis C-C, in a direction away from the branch passage 34, as represented by N, is equivalent to the size of the diameter overlap O where the diameter of the upstream fuel passage portion 140 is the same as the diameter of the downstream fuel passage portion 142 and where the axes B-B, C-C are parallel. However in other configurations these dimensions N, O may be different, whilst still realizing the same benefits of the separation surface. By way of further example, Figure 8 is an embodiment of the invention in which the upstream axis B-B is angled or inclined relative to the downstream axis C-C. In this example the diameters of the upstream and downstream fuel passage portions 140, 142 are equal. As for the previous embodiment, the extent of the diameter overlap O defines a separation surface 146 for fuel at the lower surface of the upper housing 18 (i.e. at the interface 29 with the lower housing 26). At the point where the upstream axis B-B intercepts the interface 28, the upstream axis B-B is offset laterally from the point where the downstream axis C-C intercepts the interface 28, so that that the internal surface S140 of the upstream fuel passage portion 140 is further from the inlet 44 than the internal surface S142 of the downstream fuel passage portion 142, by an amount N. In other words, the point where the upstream axis B-B intercepts the interface 28 is further from the inlet 44 than the point where the downstream axis C-C intercepts the interface 28. Likewise, a point of intersection between the upstream axis B-B and the branch axis D-D is displaced further from the inlet 44 than a point of intersection between the downstream axis C-C and the branch axis D-D, measured along the branch axis.

[0047] A further embodiment is shown in Figure 9, where the axis of the branch passage D-D is inclined relative to the axes of the upstream and downstream fuel passage portions 240, 242. This embodiment is equivalent to the prior art fuel injector section shown in Figure 2. In this embodiment, the axes B-B, C-C of the upstream fuel passage portion 240 and the downstream fuel passage portion 242 respectively are in parallel, as for Figure 6, except that the form of the upstream fuel passage portion 240 is different. Here, the upstream fuel passage portion 240 is defined within the upper housing part 18 and is of uniform diameter, but the interface with the downstream fuel passage portion 242 is defined within the upper housing part 18 rather than at the interface of the housing parts. The downstream fuel passage portion 242 includes an enlarged diameter region which defines an enlarged volume 242a with which the inlet 44 of the branch passage 34 communicates. The upstream fuel passage portion 240 defines an internal surface S240 in the upper housing part 18, as before, and the downstream part of the downstream fuel passage portion 242 defines an internal surface S242 in the lower housing part. The surfaces S240, S242 are parallel, but not aligned. A further difference in Figure 9 is the nature of the branch passage 34 which extends along the axis D-D at an angle of inclination relative to the axes B-B and C-C. As before, the upstream axis B-B is offset laterally relative to the downstream axis C-C so that the two axes are not aligned (but remain parallel), with the surface S240 of the upstream fuel passage portion 240 being spaced further from the inlet 44 than the surface S242 of the downstream fuel passage portion 242. Correspondingly, the upstream axis B-B is spaced further from the inlet 44 than the downstream axis C-C, measured along the branch axis D-D. In other words, the axes are oriented such that the intersection between the axis D-D and the axis C-C is closer to the inlet 44 than the intersection between the axis B-B and the axis D-D, measured along the axis D-D.

[0048] As a result of this configuration of passages in Figure 9, an exposed surface 246 of the housing 18 is defined by the diameter overlap O, within the housing part 18, to define a separation surface for the flow through the main flow passage. As for the previous embodiments, the diameter overlap O creates a small region of flow separation at the inlet 44 of the branch passage 34, resulting in particles with a sufficiently high Stokes number being unable to follow the sharply turning fluid past the separation surface 246 towards the branch passage 34. Instead these particles detach from the flow to follow the main flow through the enlarged volume 242a and downstream fuel passage portion 242 and towards the injector outlet. As before the branch passage 34 delivers fuel to a control valve of the injector, but without the risk of damaging particles becoming entrained in the branch flow.

[0049] Figure 10 shows a further embodiment of the invention where the main flow passage is not defined by upstream and downstream fuel passage portions defined entirely within separate housings. In this case, the upstream fuel passage portion 340 is formed in a housing 18 and defines an axis B-B. The branch passage 34 is formed in the same housing part 18, but is not defined by a groove in the surface of the housing part 18 but instead is defined by a drilling through the housing part 18. Here, however, the downstream fuel passage portion, identified as 342, is defined by an internal cavity between an outer annular housing part 348 and a central turret or projection 318 formed on the housing part 18. The turret 318 is of annular form and receives the upper end of the valve needle 16. The downstream fuel passage portion 342 has a greater flow diameter than the flow diameter of the upstream fuel flow passage portion 340. The axis represented by C-C merely represents the axis of the fuel flow through the annular turret 18, in the cross section of the figure. The axes B-B, C-C are aligned. An exposed separation surface 346 is defined by a surface of the housing part 18 (i.e. on a shoulder of the housing part 18 which connects with the turret 318). The separation surface 346 faces away from the incoming flow through the upstream flow passage portion 240.

[0050] One difference in the embodiment in Figure 10, compared to previous embodiments, is that the inlet 44 to the branch passage 34 communicates with the downstream fuel passage portion 342 at a point axially displaced (in the direction of the axis C-C) from the separation surface 346.

[0051] Figure 11 is a further embodiment of the invention, similar to Figure 6 except that the diameter of the upstream fuel passage portion 440 is not the same as the diameter of the downstream fuel passage portion 442. In this case the upstream fuel passage portion 440 is of smaller diameter than the downstream fuel passage portion 442. In addition, the upstream fuel passage portion 440 has an upstream relatively large diameter region which transitions via a frusto-conical region 452 into a relatively narrow diameter region 454. The relatively narrow diameter region 454 communicates with the downstream fuel passage portion 442 at the interface 29. The branch passage 34 is defined by a groove in the upper surface of the lower housing 26 and opens into the downstream fuel passage portion 442. The upstream axis B-B is offset laterally from the downstream axes C-C so that they are misaligned, but parallel, and with the axis B-B closer to the inlet 44 of the branch passage 34 than the axis C-C. This configuration of the axes and the fuel passage portions means that a separation surface 446 is defined by the lower surface of the upper housing part 18. Because the upstream and downstream fuel passage portions 440, 442 are of different diameter, even though the axes B-B, C- C are offset relative to one another, the surfaces S440, S442 of the upstream and downstream fuel passage portions 440, 442 are substantially aligned.

[0052] The separation surface 446, which is defined by the presence of the offset N together with the diameter of the passage 454, provides the aforementioned advantage that there is a small region of flow separation at the inlet 44 of the branch passage 34. This results in particles with a sufficiently high Stokes number being unable to follow the sharply turning fluid past the separation surface 446 towards the branch passage 34. Instead these particles detach from the flow to follow the main flow into the downstream fuel passage portion 442 and towards the injector outlet. As before the branch passage 34 delivers fuel to a control valve of the injector, but without the risk of damaging particles becoming entrained in the branch flow.

[0053] It will be appreciated that the required extent of the diameter overlap is achieved either by varying N or the diameter of the fuel passage 454, or both.

[0054] In the case where the downstream fuel passage portion 142 has a smaller diameter than the upstream fuel passage portion 140, the flow will accelerate on approach to the intersection and a smaller overlap may be required to produce the same benefit. If the downstream fuel passage portion 142 is of larger diameter (as in Figure 11), the flow will be decelerating on approach to the intersection and so a larger overlap is required. Also there is more space for the overlap O to be accommodated.

[0055] It will be appreciated that further embodiments of the invention are envisaged without deviating from the scope of the appended claims. For example, although the invention is described in the context of a main fuel supply passage through an injector it will be appreciated that it is equally applicable to any fuel supply passage / branch passage in any location within the injector.

Claims

CLAIMS1. A fuel injector (10) for an internal combustion engine, the fuel injector comprising; a fuel injector inlet (30), a fuel injector outlet and a housing (18, 26; 18, 318, 348); a fuel supply passage (32) defined within the housing (18, 26; 18, 318, 348) between the fuel injector inlet (30) and the fuel injector outlet and comprising an upstream fuel passage portion (140; 240; 340; 440) and a downstream fuel passage portion (142; 242; 342; 442), the upstream fuel passage portion defining an upstream axis (B-B) aligned with the direction of fuel flow through the upstream fuel passage portion and the downstream fuel passage portion defining a downstream axis (C-C) aligned with the direction of fuel flow through the downstream fuel passage portion, a branch passage (34) comprising an inlet (44) which opens into the fuel supply passage (32) so that a first proportion of fuel flow through the upstream fuel passage portion flows into the branch passage (34), the branch passage (34) defining a branch axis (D-D); and a separation surface (146; 246; 346; 446) defined within the fuel supply passage (32) which spaces the inlet (44) from the upstream fuel passage portion (140; 240; 340; 440) such that a proportion of the flow through the upstream fuel passage portion (140; 240; 340; 440) deflects away from the upstream axis (B-B), past the separation surface (146; 246; 326; 446), before the first proportion of the flow enters the inlet (44) and a second proportion of the flow flows downstream to the downstream fuel passage portion (142; 242; 342; 442).

2. The fuel injector as claimed in claim 1 , wherein the upstream axis (B-B) is displaced laterally relative to the downstream axis (C-C), along the branch axis (D-D), to define the separation surface (146; 246; 346; 446), and wherein the separation surface defines a maximum overlap dimension (O)which is between 10-15% of the diameter of the downstream fuel passage portion (142; 242; 342; 442).

3. The fuel injector as claimed in claim 1 or claim 2, wherein the maximum overlap dimension (O) defines an overlap cross sectional area which is no more than 30% of the cross sectional flow area of the downstream fuel passage portion (142; 242; 342; 442).

4. The fuel injector as claimed in any of claims 1 to 3, wherein the main housing comprises an upstream housing part (18) within which the upstream fuel passage portion (140; 340; 440) is defined, at least in part, and a downstream housing part (26) within which the downstream fuel passage potion (142; 342; 442) is defined, at least in part, and wherein the separation surface (146; 246; 446) is defined at an interface (29) between the upstream and downstream housing parts (18, 26).

5. The fuel injector as claimed in claim 4, wherein the separation surface (146; 246; 346) is defined by a lower surface of the upstream housing part.

6. The fuel injector as claimed in any of claims 1 to 4, wherein the separation surface (246) is defined within the upstream housing part (18).

7. The fuel injector as claimed in any of claims 1 to 6, wherein the upstream axis (B-B) and the downstream axis (C-C) are parallel with one another.

8. The fuel injector as claimed in any of claims 1 to 6, wherein the upstream axis (B-B) is inclined relative to the downstream axis (C-C).

9. The fuel injector as claimed in any of claims 1 to 8, further comprising a control valve for the valve needle, wherein the branch passage (34) is configured to deliver fuel from the fuel supply passage (32) to the control valve.

10. The fuel injector as claimed in claim 1 or claim 2, wherein the upstream axis (B-B) and the downstream axis (C-C) are coaxial and wherein the upstreamfuel passage portion (340; 440) has a different diameter to the downstream fuel passage portion (342; 442).

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