WO2017085124A1

WO2017085124A1 - Fuel injector

Info

Publication number: WO2017085124A1
Application number: PCT/EP2016/077857
Authority: WO
Inventors: Philippe Legrand
Original assignee: Delphi International Operations Luxembourg S.À R.L.
Priority date: 2015-11-17
Filing date: 2016-11-16
Publication date: 2017-05-26
Also published as: GB201520206D0; JP6806783B2; JP2018537621A; CN108291508B; EP3377753B1; EP3377753A1; CN108291508A

Abstract

A direct acting fuel injector (10) for use in an internal combustion engine, the injector comprising an actuator (20); a hydraulic amplifier chamber (31) for fuel; a valve needle (14) movable within a bore (16) provided in an injector housing having a lower housing region (18a) of a first, reduced diameter (Dnoz) and an upper housing region (18b, 18c) of a second, greater diameter, wherein the upper housing region (18b, 18c) is received within a cap nut (54) of the injector, the valve needle (14) having a surface (14c) with a needle diameter (Dnoz) exposed to fuel within the hydraulic amplifier chamber (31); and a plunger (30) having a plunger diameter (Dpc) exposed to fuel within the hydraulic amplifier chamber (31), the plunger (30) being actuable by means of the actuator (20) to provide a force to the valve needle (14) with an amplification factor determined by the ratio of the plunger diameter (Dpc) to the needle diameter (Dnoz). The hydraulic amplifier chamber (31) is defined within a region of the lower housing region (18a) external to the cap nut (54).

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

Both indirect and direct acting injectors are known for use in fuel injection systems. In an indirect acting injector, a control valve arrangement is operable to control the pressure of fuel within a control chamber which acts on an upper end of an injector valve needle. The pressure level within the control chamber determines the balance of forces on the needle, and hence controls the precise timing of needle movement away from the seating for the valve needle to commence injection. An actuator such as an electromagnetic actuator controls the control valve arrangement. The force applied by the actuator is not linked directly to the valve needle movement, but controls the control valve arrangement which in turn controls the force which is consequently applied to the valve needle via a hydraulic circuit.

In a direct acting injector, an actuator is coupled directly to the valve needle to control needle movement. Both piezoelectric and electromagnetic direct acting injectors are known. In an electromagnetic direct acting injector, a solenoid- operated actuator controls movement of a plunger, having a plunger diameter, by applying a current through a solenoid. The plunger acts on a chamber of fuel arranged at the upper end of a valve needle of a second, reduced diameter. The arrangement acts as a hydraulic amplifier arrangement by which the force of the plunger is transmitted to the valve needle with an amplification factor determined by the ratio of the plunger diameter to the diameter of the valve needle. As the plunger is actuated and pulled upwards, the volume of the chamber increases causing fuel pressure within the control chamber to reduce and hence reducing the force tending to act to seat the valve needle. If the actuation force is removed by removing or reducing the current applied to the solenoid, the plunger moves downwardly under a spring force, reducing the volume of the control chamber and increasing fuel pressure in the control chamber so as to seat the valve needle. Direct acting solenoid injectors are of interest for use in fuel injection systems because need for the additional parts and cost of the control valve arrangement of an indirect acting injector are avoided. In addition, such injectors avoid the need for a return flow path for fuel, as required for an indirect acting injector, which reduces system cost. This also reduces the dissipated energy loss and temperature, and so greatly improves overall system efficiency. However, existing injectors of this type have internal volume limitations which can lead to problems with pressure waves in the injector. The multi-injection modes that are required for some injection regimes, which require close-timed injection events, cannot therefore be realised easily. Moreover, dilation effects occur at the high fuel pressures required for modern fuel injection systems (typically 2500-3000 bar) which can lead to wear problems in current direct acting injectors for diesel engines.

It is an object of the invention to provide a direct acting injector which addresses the shortcomings of the prior art.

Summary of the invention

Accordingly, the present invention provides a direct acting fuel injector for use in an internal combustion engine, the fuel injector comprising an actuator; a hydraulic amplifier chamber for fuel; a valve needle movable within a bore provided in an injector housing having a lower housing region of a first, reduced diameter (Dnoz) and an upper housing region of a second, greater diameter, wherein the upper housing region is received within a cap nut of the injector, the valve needle having a surface with a needle diameter (Dnoz) exposed to fuel within the hydraulic amplifier chamber. The injector further comprises a plunger having a plunger diameter (Dpc) exposed to fuel within the hydraulic amplifier chamber, the plunger being actuable by means of the actuator to provide a force to the valve needle with an amplification factor determined by the ratio of the plunger diameter (Dpc) to the needle diameter (Dnoz). The hydraulic amplifier chamber is defined within a region of the lower housing region external to the cap nut.

By reference to the hydraulic amplifier chamber being "external to the capnut", it is intended to mean that the hydraulic chamber lies axially beneath a lower surface of the capnut which seals against the cylinder head, but not necessarily beneath any extension feature on the capnut (e.g. which may be provided for heat exchange purposes). The injector is advantageous because only a relatively short length valve needle is required, which improves the responsivity of the injector, and permits accurate control of injection events, especially close-timed events. Furthermore, movement of the valve needle can be controlled conveniently by means of a guide member which locates within the bore in the vicinity of the hydraulic amplifier chamber.

The hydraulic amplifier chamber is preferably defined within the guide member (i.e. both the hydraulic amplifier and the guide member are relatively close to the tip of the needle, near the outlets of the injector).

The guide member and/or the adjacent region of the bore may be provided with flats or grooves to permit fuel flow past the guide member towards outlets of the injector during injection. In one embodiment, the guide member is press fitted into the bore. The guide member conveniently includes a cylindrical region and an upper flange region, where the upper flange region guides the plunger of the injector and the cylinder region guides the valve needle, the upper flange region defining a narrower diameter than the cylindrical region.

In one embodiment, the guide member may be welded into the bore.

The guide member may be held in position or supported by a tubular member located within the bore. For example, the tubular member may be press fitted within the bore or may be welded within the bore. If the tubular component is welded within the bore, one or more weld points for the tubular member may be arranged at an end of the tubular member remote from the guide member. For example, the or each weld point for the tubular member may be provided at a step in the bore.

The tubular member may be provided with at least one flow passage to permit an unrestricted flow of fuel downstream towards the guide member.

Conveniently, the actuator may be an electromagnetic actuator, although other actuation means are envisaged.

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 present invention may be more readily understood, an example of the invention will now be described in detail with reference to the accompanying drawings in which:

Figure 1 which is a schematic cross section of a direct acting fuel injector of a first embodiment of the invention; Figure 2 is an enlarged view of the end of the fuel injector in Figure 1 ;

Figure 3 is a cross section, taken along a plane (A-A as shown in Figures 1 and 2) perpendicular to the longitudinal axis of the valve needle or the injector in Figure 1 , to illustrate a guide for the valve needle; and Figure 4 is a schematic cross section of a direct acting fuel injector of a second embodiment of the invention.

Detailed description

For the purpose of the following description it will be appreciated that references to upper, lower, upward, downward, above and below, for example, are not intended to be limiting and relate only to the orientation of the injector as shown in the illustration.

The present invention relates to a fuel injector 10 of the type generally shown in Figure 1 and 2. The injector 10 is suitable for use in a fuel injection system of an internal combustion engine, and particularly a diesel engine in which fuel is typically injected into the engine at high pressure levels in excess of 2000 bar, and as commonly as high as 3000 bar.

The injector 10 includes an injection nozzle 12 at its lower end including a valve needle 14 which is slidable within a blind bore 16 provided in an injection nozzle housing 18 under the influence of an actuator, referred to generally as 20, which also forms a part of the injector. The valve needle 14 is engageable with a valve needle seating (not identified), defined at the blind end of the bore 16, to control the flow of fuel from the injector into a combustion chamber of the engine. Fuel under high pressure is delivered to an internal injector volume 22 defined within the bore 16 through a high pressure supply passage (to be described later). The internal injector volume 22 includes an upper region 22a of enlarged diameter.

The injection nozzle housing 18 includes a lower region 18a of reduced diameter compared to a mid region 18b of the injection nozzle housing of enlarged diameter, with an intermediate region 18c of the nozzle housing, of intermediate diameter, separating the two regions 18a, 18b. A step 18f is defined between the mid and intermediate regions 18b, 18c. An upper region 18d of the injection nozzle housing 18 is of still further enlarged diameter compared to the mid region 18b. Finally, a top region 18e of the injection nozzle housing forms a small upstand on top of the upper region 18d. The lower region 18a of the injection nozzle housing is provided with a plurality of outlets (not shown) downstream of the valve needle seating to permit a flow of fuel from the internal injector volume 22 into the combustion chamber when the valve needle 14 is unseated.

As can be seen especially in Figure 2, the valve needle 14 is of relatively short length and includes a lower tip region 14a of a relatively small diameter which seats against the valve needle seating. The valve needle seating has a diameter Dseat and an equivalent surface area taken through a plane perpendicular to the longitudinal valve needle axis of SDseat. An upper region 14b of the valve needle is of relatively large diameter compared to the lower tip region 14a. The upper region 14b of the valve needle has a diameter DNoz and defines an upper end surface 14c having a surface area SDNoz. Between the tip region 14a and the upper region 14b of the valve needle, the valve needle is provided with a thrust surface which experiences an upwardly directed force, tending to urge the valve needle away from the valve needle seating, due to the surrounding fuel pressure within a lower chamber 24.

Referring also to Figure 3, an annular guide member 26 is located within the bore 16 and provides a guiding function for the upper region 14b of the valve needle as is moves towards and away from the valve needle seating. The guide member 26 includes a lower cylinder (no reference number) with an annular flange (no reference number) provided at the upper end. The internal diameter of the cylinder is greater than the internal diameter of the flange, so that the flange extends radially further inwards than the cylinder. The outer diameter of the guide member is relatively uniform, although with the option of a slightly enlarged diameter (not visible in Figure 1 ) of the annular flange. The internal surface of the bore 16, in the region of the guide member, is provided with a plurality of flats or grooves 28 to permit fuel to flow between the internal injector volume 22 and the lower chamber 24, past the guide member 26, and onwards to the outlets when the valve needle is unseated. The internal diameter of the cylinder of the guide member 26 provides the guiding function for the valve needle region 14b, in use, as the valve needle is caused to move.

The guide member 26 is typically welded into the bore 16 or is press fitted into the bore 16 in a position which defines the stroke of the valve needle 14. If the guide member 26 is welded into the bore 16, the weld can be made through the nozzle housing 18 with local weld dots at weld points. The weld points are provided in the vicinity of the flange on the guide member 26 so as to minimise any distortion of the guide member in the region where the valve needle 14 slides.

In an alternative embodiment (not shown) the internal surface of the bore 16 is not provided with any features to permit a flow of fuel, and instead the outer circumference of the guide member 26 is provided with flats or grooves for this purpose.

A plunger 30 is also received within the bore 16 and is positioned above the valve needle 14, with the lower tip region of the plunger 30 being guided by the internal diameter of the flange region at the upper end of the guide member 26. The guide member therefore provides a guiding function for both the valve needle 14 and the plunger 30. The plunger 30 is spaced apart from the upper surface 14c of the valve needle 14 to define a space therebetween which defines a chamber 31 (which may be referred to as the amplifier chamber 31 ) for receiving fuel. The chamber 31 is located in a region of the injection nozzle housing 18 that is relatively close to the valve needle seating and resides within the reduced diameter region of the nozzle housing (i.e. the lower region 18a). The plunger 30 includes a lower region 30a of relatively short length and relatively small diameter, with a first diameter Dpc, compared to an upper region 30b of relatively large length and relatively large diameter. A thrust surface of the plunger, between the upper and lower regions 30a, 30b, experiences an upward force, tending to urge the plunger 30 away from the valve needle seating, due to fuel pressure within the internal injector volume 22. The diameter of the plunger, Dpc, is smaller than the diameter of the upper surface 14c of the valve needle, DNoz. Of significance is the surface area of the end of the plunger, SDpc, at its lower end 30a, compared to the surface area of the upper surface 14c of the valve needle, SDNoz, as will be described in further detail below. The plunger 30 carries a lower spring seat 32, which resides in the enlarged chamber region 22a of the internal injector volume 22. The lower spring seat 32 is of annular form and defines an abutment surface for a spring 36 which tends to urge the valve needle 14 towards the valve needle seating. An upper spring seat 34 is received within an upper region of the enlarged chamber region 22a. The upper spring seat 34 is shaped to define a guide portion 34a for the upper region 30b of the plunger and also an abutment surface for the upper end of the spring 36. The upper spring seat is shaped to define a clearance with the plunger which provides a flow path for fuel into the enlarged chamber region 22a. The guide portion 34a is defined by an annular flange or upstand provided at the lower end of the spring seat 34.

The electromagnetic actuator arrangement 20 provided at the upper end of the injector serves to actuate plunger movement and, consequently, movement of the valve needle 14. The actuator 20 is housed partly within the lower injection nozzle housing 18 and partly within an upper injection nozzle housing 38. The actuator 20 includes a first magnetic piece 40 which resides within the upper spring seat 34 and is spaced, by a fuel-filled gap 42, from a second magnetic piece 44 upstream of the first magnetic piece 40. The first magnetic piece 40 is attached to the upper end of the plunger 30 and includes an angled drilling 46. The second magnetic piece 44 is fixed within the upper injection nozzle housing 38 and is provided with a vertical drilling 48. Together with the gap 42 and the angled drilling 46, the vertical drilling 48 defines a flow path for high pressure fuel flowing into the injector from a high pressure fuel supply (e.g. a common rail) into the enlarged chamber region 22 of the internal injector volume 22 and downstream towards the valve needle 14.

The lower surface of the upper injection nozzle housing 38 and the upper surface of the lower injection nozzle housing 18 are both of stepped form to define a region therebetween for housing a solenoid coil or winding 50 which forms a part of the actuator 20. Radially inward of the winding 50, an annular non-magnetic piece or ring 52 is also housed in this region. The annular non magnetic piece 52 closes the gap 42 at its radially outer edge to prevent fuel leakage.

The lower injection nozzle housing 18, the upper housing 38 and the actuator are housed within a cap nut 54 to retain the parts securely in position relative to one another. The lower surface 54a of the cap nut defines a sealing surface with the cylinder head (not shown) within which the injector is mounted. It is known to provide an extension on the cap nut (for example, for heat exchange purposes), but this does not alter the position of the surface 54a which seals against the cylinder head and can be considered as the lower sealing surface of the cap nut 54. In operation of the injector, valve needle movement is controlled by controlling the current that is applied to the winding 50 of the actuator 20. When a current is applied to the winding 50, an electromagnetic field is generated which attracts the first magnetic piece 40 towards the second magnetic piece 44, and therefore pulls the first magnetic piece 40 upwards, pulling the plunger 30 with it against the force of the spring 36. As the plunger 30 is pulled upwardly the volume of the chamber 31 between the lower end of the plunger 30 and the upper surface 14c of the valve needle 14 is increased so that the pressure of fuel within the chamber 30 decreases. As a result, the downward force acting on the upper surface 14c of the valve needle 14 is reduced and the valve needle 14 starts to lift. The force of the plunger 30 is amplified by fuel pressure within the chamber 31 due to the different ratios of the lower end of the plunger 30 and the upper end surface 14c of the valve needle 14, with an amplification factor determined by the ratio of SDpc to SDNoz. Once the valve needle 14 has lifted away from the valve needle seating, fuel that is delivered to the lower chamber 24 is able to flow out through the outlets into the combustion chamber.

When it is required to terminate injection, the current applied to the winding is removed, thereby reducing the force applied to the plunger 30. As a result, the plunger is caused to moved downwards, under the influence of the spring 36, reducing the volume of the chamber 31 between the end of the plunger 30 and the valve needle 14 and causing fuel to be increased in the chamber 31 . The increased fuel pressure in the chamber 31 results in an increased force being applied to the valve needle 14 which overcomes the upwardly directed forces acting on the thrust surface of the valve needle and causes the valve needle 14 to be seated, terminating injection through the outlets.

By controlling the current that is applied to the winding, injection can therefore be controlled to deliver single or multiple injections of fuel accurately.

It is one benefit of the invention that the valve needle is very short, and hence the mass of the valve needle is small. This enables the valve needle to be moved rapidly and with good control, which is especially important when there is a requirement for close-spaced injections. The plunger tip is also relatively narrow, and of low mass, and is narrower than the valve needle 14 so the necessary force amplification is provided by the chamber 31 . It is possible to make the valve needle 14 with low mass because the amplifier chamber 31 is located very close to the lowermost end of the injection nozzle housing 18, which is that region 18a of the nozzle housing 18 that is of relatively narrow diameter. Typically the valve needle has a diameter as small as 2.5mm, compared to between 3.5mm and 4mm which is typical in a prior art injector.

The short length of the valve needle 14 and the low position of the amplifier chamber 31 in the bore 16 contrasts with known direct acting injectors in which the amplifier chamber 31 resides at a much higher axial position within the nozzle housing 18, and usually within the mid region 18c of the nozzle housing 18 which has a much larger diameter. This means that in the present invention the amplifier chamber 31 adopts a position along the axis of the valve needle which falls outside the envelope of the cap nut 54 (axially beneath the lower end of the cap nut 54) which holds the injector parts together.

Referring to Figure 4, in another embodiment of the invention the guide member for the valve needle is held in position or supported within the bore 16 by means of a relatively long, tubular component 60 which lines the bore 16 along the length of the lower region 18a of the nozzle housing 18, through the intermediate region 18c and part way into the mid region 18b. An upper annular flange of the tubular component 60 abuts a step 62 in the bore 16 within the internal injector volume 22, with the tubular component 60 being press fitted into the bore 16 along its entire length and over the step 62. The tubular component 60 is provided with a plurality of openings 66 which permit fuel to flow from the volume between the tubular component 60 and the plunger 30 towards the grooves or flats 28 provided on the guide member 26 (and/or in the surface of the bore 16), and hence onwards to the lower volume 24.

The injector in Figure 4 operates the same way as for the injector in Figure 1 , with the plunger 30 and the valve needle 14 forming part of a hydraulic amplifier arrangement together with the chamber 31 . As before, the chamber 31 is defined within that region 18a of the nozzle housing which is of relatively small diameter, and which resides external to (i.e. beneath) the cap nut 54 which retains the upper injector components together. This embodiment may have benefits over that in Figure 1 in which the guide member 26 is welded into the bore 16, in that any stress concentration introduced by the weld spots is avoided by virtue of the tubular component 60 which supports the guide member 26. If the tubular component 60 is welded into the bore 16, this can be achieved at a higher axial position, for example, in the region of the step 62 where the bore 16 opens into the enlarged chamber 22a, and so any stress concentration is removed from the vicinity of the valve needle 14.

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.

Claims

Claims:

1 . A direct acting fuel injector (10) for use in an internal combustion engine, the fuel injector comprising:

an actuator (20);

a hydraulic amplifier chamber (31 for fuel;

a valve needle (14) movable within a bore (16) provided in an injector housing having a lower housing region (18a) of a first, reduced diameter (Dnoz) and an upper housing region (18b, 18c) of a second, greater diameter, wherein the upper housing region is received within a cap nut (54) of the injector, the valve needle (14) having a surface with a needle diameter (Dnoz) exposed to fuel within the hydraulic amplifier chamber (31 ); and

a plunger (30) having a plunger diameter (Dpc) exposed to fuel within the hydraulic amplifier chamber (31 ), the plunger (30) being actuable by means of the actuator (20) to provide a force to the valve needle (14) with an amplification factor determined by the ratio of the plunger diameter (Dpc) to the needle diameter (Dnoz);

wherein the hydraulic amplifier chamber (31 ) is defined within a region of the lower housing region ( 18a) external to the cap nut (54).

2. The fuel injector (10) as claimed in claim 1 , wherein the valve needle (14) is guided within the bore (16) by means of a guide member (26).

3. The fuel injector (10) as claimed in claim 2, wherein the guide member (26) includes a first region which guides the plunger (30) and a second region which guides the valve needle (14).

4. The fuel injector as claimed in claim 2 or claim 3, wherein the hydraulic amplifier chamber (31 ) is defined within the guide member (26).

5. The fuel injector as claimed in any of claims 2 to 4, wherein the guide member (26) and/or the adjacent region of the bore is provided with flats or grooves (28) to permit fuel flow past the guide member (26) towards outlets of the injector during injection.

6. The fuel injector as claimed in any of claims 2 to 5, wherein the guide member (26) is press fitted into the bore.

7. The fuel injector as claimed in any of claims 2 to 6, wherein the guide member (26) is welded into the bore.

8. The fuel injector as claimed in any of claims 2 to 7, wherein the guide member (26) is held in position by a tubular member (60) located within the bore (16).

9. The fuel injector as claimed in claim 8, wherein the tubular member (60) is press fitted within the bore (16).

10. The fuel injector as claimed in claim 9, wherein the tubular member (60) is welded within the bore (16).

1 1 . The fuel injector as claimed in claim 10, wherein at least one weld point for the tubular member (60) is at an end of the tubular member (60) remote from the guide member (26).

12. The fuel injector as claimed in claim 1 1 , wherein the or each weld point for the tubular member (60) is at a step in the bore (16).

13. The fuel injector as claimed in any of claims 8 to 12, wherein the tubular member (60) is provided with at least one flow passage (66) to permit an unrestricted flow of fuel downstream towards the guide member (26).

14. The fuel injector as claimed in claim 13, wherein the first region of the guide member (26) is a flange provided at an upper end of the second region of the guide member (26).

15. The fuel injector as claimed in any of claims 1 to 14, wherein the actuator (20) is an electromagnetic actuator.