GB2549479A

GB2549479A - Fuel injector

Info

Publication number: GB2549479A
Application number: GB1606715.9A
Authority: GB
Inventors: Bonfigli Fabrizio; Demas Mathieu
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2016-04-18
Filing date: 2016-04-18
Publication date: 2017-10-25

Abstract

A fuel injector 20 for use in an i.c. engine, eg a compression ignition engine, includes an injection valve member 28 having a control surface 48 or control surface associated therewith exposed to fluid pressure in a control chamber 40; a leaf spring element 102 extends transversely through the control chamber 40 to apply a biasing force to the control surface of the injection valve member 28. The biasing force may be applied to the centre of the control surface in line with the longitudinal axis of the valve member 28. The leaf spring 102 may be defined by a U-shaped cut-out feature 114 of a spring plate member 112 positioned between a valve guide body 44 and a control valve body (46, fig.2). The leaf spring element may engage an anti-spin feature (110, fig.4) eg a slot or groove in the valve member 28.

Description

Fuel injector

Technical field

The present invention relates to a fuel injector for use in delivering high pressure fuel to an internal combustion engine. In particular, but not exclusively, the invention relates to a fuel injector for use in a compression ignition internal combustion engine.

Background

In a fuel injected engine it is necessary to have precise control over the quantities of fuel delivered by the fuel injectors to optimize combustion. This is particularly so with diesel engines where it is necessary to inject small quantities of fuel across a wide range of fuel pressures. Typically, a fuel injector includes an injection nozzle having an injection valve needle which is movable towards and away from a seating so as to control fuel injection into the engine. The injection valve needle is controlled by means of a nozzle control valve, which controls fuel pressure in a control chamber which acts on an upper end of the injector valve needle. The pressure of fuel within the control chamber determines the balance of forces on the injection valve needle, and therefore controls when the valve needle is able to lift away from its seat in order to commence fuel delivery from the nozzle.

The nozzle control valve is controlled by a suitable actuator, such as an electromagnetic or piezoelectric actuator. The force applied by the actuator does not move the injection valve needle directly, but instead controls the position of a valve member which in turn controls the force which is consequently applied to the injection valve needle via a hydraulic circuit. In addition to the force applied by the fluid pressure in the control chamber, the valve needle is biased into a closed position by a needle spring. In one known configuration of fuel injector, the needle spring is a coil spring that is housed in the control chamber and acts on the upper end of the valve needle. In an alternative configuration of fuel injector 2, as shown in Figure 1, a coil spring 4 is located in compression between a spring abutment 6 defined by a needle guide block 8 and a spring retaining shoulder 10 defined by a valve needle 12. The coil spring 4 therefore acts on the valve needle 12 in addition to the fuel in a control chamber 14 to bias the valve needle 12 into engagement with its seat (not shown).

Coil springs are widely available in many sizes and are able to be machined accurately so as to provide a consistent, accurate and precise biasing force to the valve needle. Moreover, they are cost effective. However, due to the helical shape of the valve needle, there is a risk that the seating force on the valve needle will include an angular component which may cause the valve needle to move angularly during its movement away from and towards the valve needle seat. Such an occurrence could, over time, cause the valve needle seat or the needle tip to wear excessively, which may affect spray dispersion undesirably.

It is against this background that the embodiments of the invention have been devised.

Summary of the invention

Accordingly, the embodiments of the present invention provide a fuel injector for use in an internal combustion engine, the fuel injector comprising an injection valve member having a control surface or a control surface associated therewith exposed to fluid pressure in a control chamber. The control chamber houses, at least in part, a leaf spring element that extends transversely through the control chamber and applies a biasing force to the control surface of the valve member. A benefit of the arrangement is that the leaf spring element is able to apply a force to the control surface of the valve member that is substantially in alignment with a longitudinal axis thereof. This avoids problems associated with prior art in which coil springs have been observed to cause the valve needle to move angularly during use.

The fuel injector may also include a nozzle body having a bore for receiving fuel from a supply line for pressurised fuel, spray outlets from the bore for delivering fuel to the combustion cyiinder, wherein the injection valve member. which may be in the form of a needie, but may comprise two or more components, is siidabie within the bore between a dosed position in which fuei fiow through the spray outiets into the combustion chamber is prevented, and an open position in which fuei fiow through the spray outiets into the combustion chamber is enabied. Movement of the vaive member may be controiled by varying fuei pressure within the controi chamber. Pressure controi may be through the use of a controi vaive under the controi of an actuator, which may be an eiectromagnetic actuator.

The ieaf spring eiement may act substantiaiiy in the centre of the controi surface, in some embodiments, this means that the ieaf spring eiement acts on a raised projection at the back end of the vaive member. Locating the point of action of the ieaf spring eiement as dose as possibie to the centre of the controi surface means that the force is appiied to the vaive member cioseiy in aiignment with its iongitudinai axis. in one embodiment, the ieaf spring eiement forms part of a spring piate member. The spring piate member may be shaped to have a periphery that matches adjacent fuei injector body components. For exampie, the spring piate member may be substantiaiiy circuiar.

The shape of the ieaf spring element may be defined by a cut-out feature or slot that penetrates through the body of the spring plate member. In one embodiment the cut-out feature is generally U-shaped such that the leaf spring element is defined substantially between the arms of the cut-out feature.

In the illustrated embodiment, the leaf spring element may bend away from the plane of the spring plate member. In this way the leaf spring element can be considered to ‘point towards’ the control surface of the valve member such that a distal end or ‘tip end’ of the leaf spring member contacts the control surface and applies the force to it.

In one arrangement, the spring plate member is positioned between a valve guide body, which controls axial movement of the valve member, and a control valve body, which houses an actuator for controlling pressure within the control chamber.

In principle, the spring plate member may be configured as suited to a particular application. However, in one application the spring plate member may be between 0.2mm and 0.3mm in thickness, preferably 0.25mm. Moreover, the leaf spring element may have a spring constant in the range of 15-30N/mm, preferably about 22N/mm.

To ensure that the valve member does not rotate in use, optionally the leaf spring element may be configured to engage an anti-spin feature defined by the control surface. The anti-spin feature may be defined at least in part by a projection extending from a distal end of the valve member.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.

Brief description of the drawings

In order that the invention may be more readily understood, embodiments of the invention will now be described in detail with reference to the accompanying drawings in which:

Figure 1 is a cross section of part of a known indirect acting fuel injector;

Figure 2 is a cross section of a part of a fuel injector in accordance with an embodiment of the invention;

Figure 3 is an enlarged view of the fuel injector in Figure 1 to illustrate a spring arrangement of the injection valve member of the fuel injector;

Figure 4 is a view from the upper end of the injection valve member, showing the position of the spring arrangement relative to the injection valve member and its valve guide; and

Figure 5 is a plan view of the spring arrangement of Figures 2 to 4. Detailed description

For the purpose of the following description it will be appreciated that references to upper, lower, upward, downward, above, below and so on, relate only to the orientation of the injector as shown in the accompanying figures and so such terms are not intended to be limiting.

With reference to Figure 2, a fuel injector 20 includes a nozzle arrangement 22 including a nozzle body 24 that defines a blind bore 26 within which a needle-like injection valve member 28 is slidable. In some arrangements, the valve member or needle 28 may be a single part although in other arrangements, the valve member 28 may be a composite part comprising, for example, an upper part that may be in the form of a piston that is coupled to a separate lower part which may be in the form of a needle. For present purposes however, references to a valve member and a valve needle may be considered to be synonymous.

It should be appreciated that Figure 2 only shows a part of a fuel injector 20, and also therefore only part of the nozzle body 24. However, Figure 2 also illustrates schematically the valve member 28 extending downwards such that a tip 30 of the valve member 28 is engageable with a valve seat 32 that is defined by the inner surface of the blind end of the nozzle body bore 26.

Engagement of the valve tip 30 with the valve seat 32 controls delivery of fuel through a set of nozzle spray outlets 34. At this point, it should be noted that the valve member 28 may be conventional in that it is shaped to permit fluid to flow between the valve member 28 and the inner surface of the nozzle body bore 26 towards the blind end and, thus, the spray outlets 34. The fuel injector 20 shown in Figure 2 illustrates one particular arrangement of valve member and spray outlets, although it should be appreciated that other configurations are possible.

Movement of the valve member 28 towards and away from the valve seat 32 is controlled by balancing the axial forces on the valve member 28. A control chamber 40 provides a downwards acting force on the valve member 28 whilst a counteracting force is established by conventional thrust surfaces 42 defined on the outer surface of the valve member 28.

In the illustrated injector arrangement, the control chamber 40 is defined by three components: the valve member 28, a valve guide body 44 and a control valve body 46.

The valve guide body 44 is located directly above the nozzle body 24 and defines a central barrel or ‘valve guide’ 45 which receives an upper portion of the valve member 28 so that a control surface 48 associated therewith is exposed to the control chamber 40. The valve guide body 44 thus guides the axial movement of the valve member 28 which therefore acts like a piston in the valve guide 45.

The control valve body 46 in this embodiment is a block-like component that is located above the valve guide body 44 and controls the flow of fuel out of the control chamber 40. The control chamber 40 is in fluid communication with a high-pressure fuel channel 47 through an inlet passage (not shown) for the supply of fuel.

It should be noted that Figure 2 does not show the control valve body 46 in detail, although a schematic representation of an actuator 50 and its associated valve (valve and actuator are indicated by a single reference numeral 50) are provided for completeness. The control valve body 46 may be considered to be conventional and the actuator 50 may be any suitable type of actuator, for example an electromagnetic or piezoelectric actuator, both of which would be known to the skilled person.

Although not shown in the figures, the various body parts of the nozzle arrangement 22 may be held together in a cap nut or other equivalent casing component.

It has been explained above that movement of the valve member 28 is determined by the balance of forces acting on it. The principle force that determines movement of the valve member 28 is the force due to pressure of fuel in the control chamber 40 acting on the control surface 48 of the valve member 28. Conventionally the control chamber 40 may house a coil spring arranged to bias the valve member into the closed position. The function of such a closing spring is important since it causes the valve member 28 to close more quickly at termination of injection as fuel pressure in the control chamber is re-established. Fast termination of injection is desirable as it is an important factor to optimize combustion efficiency.

In contrast to conventional configurations of fuel injector in which the closing spring would be in the form of a coil spring housed within the control chamber 40, the embodiment shown in Figure 2 to 5 comprises an alternative closing spring arrangement 100.

With reference to Figures 2 to 5, the closing spring arrangement 100 comprises a spring element 102 that extends transversely into the control chamber 40 at a downward angle to act on the control surface 48 of the valve member 28 thereby applying a biasing force thereto. The spring element 102 is therefore housed, at least in part, within the internal volume defined by the control chamber 40. In effect, therefore, the leaf spring element 102 can be considered to be cantilevered from the edge of, and thus projects into, the control chamber 40.

In use, in the position shown in Figure 2, the valve member 28 is biased in the closing direction by the spring element 102 and by the high fuel pressure in the control chamber 40, such that the valve tip 30 engages the valve seat 32 and delivery of fuel from the fuel injector does not occur. These biasing forces are greater than the hydraulic forces acting on the valve member 28 in the nozzle body 24, for example on the thrust surfaces 42. In order to lift the tip 30 of the valve member 28 away from the valve seat 32 to permit fuel to be delivered from the fuel injector 20, the actuator 50 is energized which operates the associated control valve. Such lifting of the control valve permits fuel to escape from the control chamber 40 through an outlet channel (not shown) and to drain through the control valve body 44, hence causing a pressure reduction in the control chamber 40. The valve member 28 will then lift from its valve seat 32 when the upwards force (i.e. the force due to fuel pressure) acting on the valve member 28 at the thrust surfaces 42 becomes greater than the fuel force in the control chamber 40 and the spring force.

In order to terminate delivery, the actuator 50 is de-energized such that the control valve stops the draining of fuel from the control chamber 40, which causes the pressure within the control chamber 40 to build up again to the level of the high pressure channel 47. This causes the valve member 28 to re-engage the valve seat 32 thereby terminating fuel injection.

The closing spring arrangement 100 will now be described in more detail. The spring element 102 is generally linear and can be considered to be in the form of a blade or a leaf spring. Hereinafter it will be referred to as ‘leaf spring element’ 102. A distal or ‘tip’ end 104 of the leaf spring element 102 acts in a central region 106 of the control surface 48 and therefore applies a closing force to the valve member 28 in a direction that is substantially in alignment with its longitudinal axis L. In particular, the leaf spring element 102 engages with the top of a protruding reduced diameter portion 108 of the valve member 28. Significantly, the leaf spring element 102 does not apply an angular force component to the valve member 28 which avoids the problems that have been explained above in connection with coil springs. To ensure that the valve member 28 does not rotate, optionally the reduce diameter portion 108 of the valve member 28 may include an anti-spin feature 110 such as a slot or groove, that can be seen particularly well in Figure 4. The leaf spring element 102 is thus able to block excessive angular movement of the valve member 28 by the sides of the leaf spring element 102 coming into contact with the slot anti-spin feature 110.

In this embodiment, the leaf spring element 102 is an integral part of a spring plate member 112. The spring plate member 112 is substantially flat and so is only seen partially in Figure 2. However, it can be seen that the spring plate member 112 has an outer dimension that is comparable to the diameter of the valve guide body 44, and is sandwiched between the valve guide body 44 and the control valve body 46. Notably, the leaf spring element 102 bends out of plane of the spring plate member 112 towards the top of the valve member 28.

Referring also to Figure 4 and 5, the spring plate member 112 is circular in form, somewhat like a washer or shim, although it will be appreciated that this precise shape is not essential. To define the leaf spring element 102, the spring plate member 112 is penetrated by a generally U-shaped slot or cut-out feature 114, hereinafter simply ‘slot’, such that the leaf spring element 102 is defined between arms 114a of the slot 114. Due to its characteristic shape, the leaf spring element 102 could also be referred to as blade-like, strip-like, tongue-like, or arm-like in form. The leaf spring element 102 extends radially inward from a base portion 101 which is located towards an edge of the spring plate member 112, in the orientation of Figure 5, such that the distal end 104 of the leaf spring element 102 is approximately at the centre of the spring plate member 112. In this embodiment, the arms 114a of the cut-out feature diverge away from one another towards either ends which provides the leaf spring element 102 with a shape that tapers outwardly in a direction away from the tip end 104 towards the base 101. Expressed another way, the lead spring element 102 is cantilevered from a base part defined towards the edge of the spring plate member 112. The widening shape of the leaf spring element 102 may reduce the tendency of it to fatigue during prolonged use.

It will be noted that the arms and the apex of the U-shaped slot 110 are shaped so that part of the spring plate member 112 overlaps the open upper end of the control chamber 40. However, this is not essential and alternate slot shapes are envisaged in which the entire open upper end of the control chamber 40 is exposed by the shaped slot 110. Irrespective of the precise shape, it should be appreciated the shaped slot 110 provides an aperture or channel through which fuel can flow out of and into the control chamber 40 from associated passages within the adjacent injector body components 44, 46.

The spring plate member 112 is convenient to manufacture since it may be formed by a simple stamping from a suitable material, for example stainless steel. Examples of suitable materials are VDSiCr (carbon spring steel) in sheet form, available from China Longhai Special Steel Co., LTD, and also Oteva® super clean steel available from Suzuki Garphyttan AB.

Currently, it is preferred, although not essential, that the spring plate member 112 is about 0.25mm in thickness which provides the leaf spring element 102 with a spring constant of approximately 22N/mm. Currently it is envisaged that the tip end 104 of the leaf spring element 102 will have an axial travel of approximately 0.3mm which will provide a closing force of about ION. Of course, it will be appreciated that the configuration of the spring plate member 112, for example its material type, thickness, outer dimension, and shape of the U-shaped slot 114 may be selected so as to tune the characteristics of the leaf spring element 102 as required. The above values are therefore provided merely to give an example of a practical embodiment in an intended fuel injector application.

Since the spring plate member 112 is positioned between the valve guide body 44 and the control valve body 46, it may be provided with apertures 120 which are to be aligned with fuel passages running through the body components. In this way, the spring plate member 112 can be integrated into existing fuel injector designs without affecting fuel flow through the body components. In this embodiment the spring plate member 112 is shown with two circular apertures 120, although it should of course be noted that the number, shape and positioning of the apertures could be altered as required for a particular application.

It will be appreciated that many modifications may be made to the above examples without departing from the scope of the present invention as defined in the accompanying claims.

For example, in the illustrated embodiment the leaf spring element 102 is defined by the larger spring plate member 112 which therefore encircles the leaf spring element 102. Although this structure is useful because the spring plate member 112 acts as a shim or space between the valve guide body 44 and the control valve body 46, such a structure is not essential. For example, it is envisaged that the leaf spring member 102 could be a single part without being defined by a cut-out feature of a larger plate. In such a design, the base of the leaf spring element could be clamped between adjacent injector body components so that the cantilevered portion of the leaf spring element extends into the control chamber. Other configurations are possible.

Although the embodiments described above refer to the use of the injector in diesel injection systems, the skilled person will appreciate that the embodiments of the invention are also applicable to gasoline injection systems.

Claims

1. A fuel injector (20) for use in an internal combustion engine, the fuel injector comprising: an injection valve member (28) having a control surface (48) or a control surface associated therewith exposed to fluid pressure in a control chamber (40); wherein the control chamber (40) houses, at least in part, a leaf spring element (102) that extends transversely through the control chamber (40) and applies a biasing force to the control surface (48) of the injection valve member (28).

2. The fuel injector (20) of claim 1, wherein the leaf spring element (102) acts substantially at the centre of the control surface (48).

3. The fuel injector (20) of claims 1 or 2, wherein the leaf spring element (102) applies a force to the injection valve member (28) that is substantially in line with a longitudinal axis (L) thereof.

4. The fuel injector (20) of any of claims 1 to 3, wherein the leaf spring element (102) forms part of a spring plate member (112).

5. The fuel injector (20) of claim 4, wherein the leaf spring element (102) is defined by a cut-out feature (114) of the spring plate member (112).

6. The fuel injector (20) of claim 5, wherein the cut-out feature (114) is U-shaped such that the leaf spring element (102) is defined substantially between arms of the cut-out feature (114).

7. The fuel injector (20) of any one of claims 4 to 6, wherein the leaf spring element (102) bends away from the spring plate member (112) so that a distal end of the leaf spring element (102) engages with the control surface (48) of the valve member (28).

8. The fuel injector (20) of any one of claim 4 to 7, wherein the spring plate member (112) is positioned between a valve guide body (44), which controls axial movement of the injection valve member (28), and a control valve body (46), which houses an actuator (50) for controlling pressure within the control chamber (40).

9. The fuel injector (20) of any one of claims 4 to 8, wherein the spring plate member (112) is between 0.2mm and 0.3mm in thickness.

10. The fuel injector (20) of any one of claims 1 to 9, wherein the leaf spring element (102) has a spring constant in the range of 15N/mm to 30N/mm.

11. The fuel injector (20) of claim 10, wherein the leaf spring element (102) has a spring constant of about 22N/mm.

12. The fuel injector (20) of any one of claims 1 to 11, wherein the leaf spring element (102) is engageable with an anti-spin feature (110) defined by the control surface (48).

13. The fuel injector (20) of any one of claims 1 to 12, wherein the control surface (48) is defined at least in part by a projection (108) extending from a distal end of the injection valve member (28).