EP3332112B1

EP3332112B1 - Injection nozzle

Info

Publication number: EP3332112B1
Application number: EP16744779.6A
Authority: EP
Inventors: Jean-Luc BEDUNEAU; Philippe Legrand
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2015-08-03
Filing date: 2016-07-28
Publication date: 2020-01-08
Anticipated expiration: 2036-07-28
Also published as: JP2018523785A; JP6794446B2; GB201513643D0; EP3332112A1; WO2017021288A1

Description

TECHNICAL FIELD

The present invention relates generally to fuel injection nozzles, and in particular to injection nozzles for supplying fuel to internal combustion engines, such as diesel engines.

BACKGROUND OF THE INVENTION

An example of a conventional injection nozzle 1 is illustrated in Figure 1. As shown, a needle 2 is arranged within an elongate hollow nozzle body 3, and the distal end or tip 4 of the needle 2 is biased into contact with a generally conical seat 5 within the nozzle body 3 by means of a compression spring 6, so as to seal the nozzle 1. The end 7 of the nozzle body 3 is provided with one or more small apertures 8 through which fuel is injected into the engine.
In use, diesel fuel is supplied to the injection nozzle 1 from a high-pressure fuel supply in the form of a common fuel rail (not shown) fed by an injection pump (not shown). The fuel passes through a channel 9 to a first fuel accumulator volume 10 arranged around the needle 2. A second fuel accumulator volume 10a is disposed downstream of the first fuel accumulator volume 10, the first and second accumulator volumes 10, 10a being separated by a flange 2a defined by an enlarged diameter portion of the needle 2. The flange 2a is sized for a relatively close fit within the body 3 such that a clearance between the flange 2a and the body 3 is small enough to create a restriction, thereby producing a pressure drop between the first and second accumulator volumes 10, 10a. This pressure drop can be used to control movement of the needle 2.
Injection of fuel from the injection nozzle 1 is controlled by an electronic control unit (not shown). The injection nozzle 1 includes a control valve (not shown) which controls the movement of the needle 2 with respect to the valve seat 5 at the tip of the injection nozzle 1. The control valve is operable to increase or decrease the fuel pressure in a control chamber 11 disposed at the upper end of the needle 2 as viewed in Figure 1, by controlling flow between the control chamber 11 and a low-pressure drain (not shown). The control chamber 11 is connected to the high-pressure fuel supply, so that the pressure in the control chamber 11 can be switched between the relatively high supply pressure and a relatively low pressure according to the position of the control valve.
When the control valve is operated to connect the control chamber 11 to drain, the pressure of fuel in the control chamber 11 decreases, and the higher pressure of fuel in the accumulator volumes 10, 10a causes the needle 2 to move away from the seat 5 of the nozzle body 3. This allows the fuel to be sprayed through the apertures 8 and enter the engine. When the control valve moves to prevent communication between the control chamber 11 and the drain, the pressure in the control chamber 11 increases back to the supply pressure. As a result, the needle 2 moves back on to the seat 5 so as to seal the injection nozzle 1 and cut off the fuel supply to the engine. To ensure that the pressure difference between the fuel in the control chamber 11 and the fuel in the accumulator volume 10a is sufficient to create an adequate closing force on the needle 2 during this closing operation, a flow restriction is included between the high-pressure supply and the accumulator volume 10a, which gives rise to a reduction in pressure in the accumulator volume 10a during needle closure, relative to the supply pressure.
In the conventional arrangement illustrated in Figure 1, the injection nozzle 1 is provided with upper and lower guiding regions 12, 13 which serve to centre the needle 2 within the nozzle body 3. Centring of the needle 2 is important in order to ensure proper functioning of the injection nozzle 1. The lower guiding region 13 is formed on either the needle 2 or on the nozzle body 3, or on both the needle 2 and the nozzle body 3 by a machining process. The upper guiding region 12 is defined by a guide piece 12a affixed to the upper end of the body 3 and having a central bore which receives an upper portion of the needle 2 and which is sized for a close fit with the needle 2, thereby providing a guiding function.
To provide timing information that enables improved control of the nozzle 1, a voltage is applied to the needle 2 using an electrical input (not shown). As both the needle 2 and the body 3 are made from electrically conductive material, an electric circuit is completed when the tip 4 makes contact with the seat 5. The voltage applied to the needle 2 then creates an output signal that is delivered to the engine control unit through an output (not shown). This output signal indicates the precise moment at which the needle 2 engages the seat 5, which is valuable data for optimising control of the nozzle in ongoing operation.
To ensure that an output signal is not generated before the needle 2 engages the seat 5, the outer surfaces of the guide regions 12, 13 are electrically insulated in areas that may contact the inner surface of the body 3.
It is desirable to ensure that the needle centres accurately on the seat 5 for various reasons. For example, inaccurate centring will result in the needle 2 making electrical contact with the body 3 before fully engaging the seat 5 to close the nozzle 1. An output signal generated in such circumstances will give a false reading of the time at which the nozzle 1 closes, which has an impact on the control of subsequent injection events. Inaccurate needle alignment can be caused, for example, by expansion of the body 3 under the action of high pressure fuel surrounding the needle so that a clearance between the needle 2 and the body 3 in the lower guide region 13 is too large for accurate guidance.
In order to achieve optimal centring of the needle 2, it is important to provide the lower guiding region 13 as close as possible to the seat 5 of the nozzle body 3. However, the closer the lower guiding region 13 is to the seat 5, the more difficult it is to machine the guiding region 13 accurately due to the dimensions of the grinding tool required.
It would therefore be desirable to provide arrangements which overcome, or at least mitigate, these disadvantages.
EP0387179 A2 discloses an injection nozzle completing an electric circuit when the needle engages the valve seat.

SUMMARY OF THE INVENTION

Thus, in accordance with the present invention there is provided an injection nozzle for an internal combustion engine, the nozzle comprising an elongate hollow body and a needle arranged to reciprocate within the hollow body to permit fuel to be dispensed to the engine from at least one aperture at a distal end of the body, the distal end of the body defining a profiled seat against which the needle is arranged to bear to seal the nozzle. The injection nozzle is characterised in that it further comprises an electrically insulating guide assembly including a guide which abuts the seat throughout reciprocating movement of the needle so as to centre the distal end of the needle within the body as needle movement is guided, the electrically insulating guide assembly being arranged to insulate the needle electrically from the body when the needle is disengaged from the seat.
By providing a separate guiding means at the distal end of the body and needle, there is no longer the need to machine the nozzle body or the needle in this region to achieve the desired centring of the needle within the body. This separate guiding means acts in conjunction with the profiled seat to achieve the desired centring function. Furthermore, such a separate guiding means can readily be machined to the desired shape prior to insertion in the nozzle body. This contrasts with the conventional arrangements in which the inner surface of the nozzle body must been machined to provide the desired guiding function.
A further advantage is that the desired relative positions of the needle and nozzle body are more readily maintained throughout repeated operation of the injection nozzle, due to the improved centring function.
Also, as the guide is surrounded by fuel, there is no pressure expansion force applied to the guide and consequently the clearance between the nozzle body and the needle will not increase with pressure. Indeed, as pressure acts on a larger external surface of the guide compared to the inner surface area, the guide may shrink slightly.
By electrically isolating the needle from the body, the electrically insulating guide assembly enables accurate timing information to be extracted, as a control signal indicating the moment at which the needle engages the seat will only be generated on engagement. This effect is enhanced by the fact that the guide centres the needle accurately, meaning that the needle makes contact with the seat in the correct place and so the control signal is not generated before the nozzle closes as in known arrangements.
The injection nozzle preferably further comprises means for biasing the guide towards the profiled seat. This may take the form of a compression spring located between the guide and a proximal end portion of the needle. Alternatively the spring may be disposed between the guide and the body of the nozzle. Such an arrangement ensures that the guide remains in contact with the profiled seat and thereby achieves the centring function at all times.
The guide may be formed from non-conductive material such that the guide insulates the needle electrically from the body when the needle is disengaged from the seat. For example, the guide may be formed substantially of plastics or ceramic. Alternatively, the electrically insulating guide assembly may comprise a layer or coating of non-conductive material on the surface of needle and/or on the inner surface of the guide, thereby to insulate the needle electrically from the body when the needle is disengaged from the seat. The layer may cover a portion of a surface of the guide or the needle, or entire surfaces. The layer may be substantially of plastics or ceramic base, for example, Al2O3 or an equivalent material, or 'Diamond-Like Carbon' coating or similar. In a further alternative, the insulator may be disposed between the guide and the body, for example as a non-conductive layer on the outer surface of the guide. The layer may cover the entire outer surface of the guide, or alternatively only a portion of the guide surface. For example, the layer may be restricted to a portion of the surface of the guide that engages the body; or a corresponding portion of a surface of the body. For enhanced electrical insulation, it is also possible for the nozzle to include both a non-conductive guide and an insulating layer between the guide and the needle.
In a preferred embodiment, the profiled seat is substantially conical. This in itself serves to centre the needle to some extent when the needle is in contact with the profiled seat, but more importantly for the purposes of the present invention also enhances the centring effect of the guide.
In this case, the guide preferably also comprises a substantially conical surface which abuts the substantially conical profiled seat. It is especially preferred that the angle of the two conical surfaces is substantially equal, so as to maximise the area of contact between the guide and the seat.
The guide may take the form of a generally tubular collar or sleeve having a substantially circular cross-section. In a preferred embodiment, the end of the collar which abuts the conical profiled seat will also be conical in shape, and the other end of the collar will be flat so as to provide a suitable surface against which the compression spring may bear.
The needle is preferably formed with at least one channel for conveying the fuel to the aperture(s), and these may conveniently be formed on the surface of the needle.
Alternatively, or in addition, the guide is preferably shaped so as to define at least one channel for conveying the fuel to the aperture(s), and in this case the channel(s) can be in the form of apertures and/or slots. The size of the cut-out areas can be selected to control the flow of the fuel so as to achieve specific desired hydraulic functions, for example nozzle path orifice or pressure wave damping.
The injection nozzle may comprise one or more further guides located at or near the proximal end of the needle and arranged to centre the proximal end of the needle. In one embodiment, the proximal end of the needle is formed with a flange portion which is cooperable with the further guide(s). This, in combination with the guide at the distal end of the needle, ensures that the needle is centred within the hollow body throughout its entire length.
This centring function of the proximal end of the needle may advantageously be achieved by forming the needle with a proximal guide portion which is arranged to slide within the hollow body, or within another component, to provide the centring function. The proximal guide portion may be a flange portion, i.e. a region of increased diameter. In one embodiment, the proximal guide portion separates a control chamber from a fuel accumulator volume.
The injection nozzle may be configured such that, in use, the fuel pressure immediately upstream of the guide is substantially equal to the fuel pressure immediately downstream of the guide. Thus, in this arrangement, the guide causes substantially no flow restriction.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic illustration of a known injector nozzle and has already been described. The present invention is now described by way of example only with reference to the remaining drawings in which:
Figure 2 is a schematic illustration of an injector nozzle according to an embodiment of the invention;
Figure 3 is a detail view of a tip region of the nozzle shown in Figure 2;
Figure 4 is a perspective view of a collar of the injector nozzle shown in Figure 2; and
Figure 5 is a schematic illustration of an injector nozzle according to another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the description of the preferred embodiments below, the terms "lower" and "upper" are used to refer to the relative positions of components of the injection nozzle as shown in the drawings, and are not in any way intended to refer to the positions or orientations of these components in use.
Referring to Figure 2, which is a schematic cross-sectional view illustrating a first embodiment, an injection nozzle 21 comprises a needle 22 arranged within an elongate hollow nozzle body 23. As with the conventional arrangement described above with reference to Figure 1, the distal end or tip 24 of the needle 22 is biased into contact with a generally conical seat 25 within the nozzle body 23 by means of a compression spring 26, so as to seal the nozzle 21. The end 27 of the nozzle body 23 is provided with one or more small apertures 28 through which fuel is injected into the engine.
As with the conventional arrangement of Figure 1, the injection nozzle 21 is provided with an upper or proximal guiding region 30, which serves to centre the needle 22 within the nozzle body 23. The proximal guiding region 30 is defined by a guide piece 42 affixed to the upper end of the body 23 and having a central bore that is sized for a close fit with the needle 22, thereby providing a guiding function. For example, a clearance of approximately 5µm may be defined between the guide piece 42 and the needle 22.
An enlarged diameter portion of the needle 22 defines a flange 43 which is sized for a close fit within the body 23. The flange 43 acts to create a restriction to fuel flow and to create a larger surface on which a force created by the resulting pressure differential will be applied for controlling needle movement. The flange 43 resides approximately mid-way between the upper end and the tip 24 of the needle 22 at the upper end of an elongate region 37 of the needle 22 of slightly enlarged diameter compared to the diameter of the needle 22 immediately upstream of the flange 43. Although not visible in Figure 2, the flange 43 of the needle 22 includes a small drilling to create the fuel restriction. Alternatively, the required restriction may be created by an appropriately sized clearance between the flange 43 and the body 23.
In addition to the proximal guiding region 30, in the present embodiment a lower or distal guide is provided downstream of the elongate region 37 of the needle 22 by means of a separate, generally tubular ring or collar 31 which functions to centre the lower part of the needle 22 within the nozzle body 23. As can be seen from Figure 2, the collar 31 is provided close to the lower end of the needle 22 to guide a region 19 of the needle 22 of reduced diameter compared to the elongate region 37. The clearance between the inner surface of the collar 31 and the needle 22 in the region 19 is typically 10µm or less, ensuring that the needle 22 is guided very accurately within the collar 31.
As shown more clearly in Figure 3, the collar 31 in this embodiment is in the form of a solid annular ring having an upper end surface 32 lying within a plane perpendicular to the axis of the collar 31 and a frusto-conical lower end surface 33 having the same cone angle as that of the conical seat 25. The lower end surface 33 therefore cooperates with the conical seat 25 such that the collar 31 is self-centring on the seat 25. In this way, the collar 31 enables effective alignment of the needle 22 within the body 23.
Returning to Figure 2, during operation, fuel is supplied to the injection nozzle 21 from a high-pressure fuel supply in the form of a common rail (not shown). The fuel passes through a channel 34 within the guide piece 42 secured at the upper end of the body 23 to a first fuel accumulator volume 29 disposed upstream of the flange 43, and on to a second fuel accumulator volume 29a disposed downstream of the flange 43.
Injection of fuel from the injection nozzle 21 is under the control of an electronic control unit (not shown). As is known in the art, a control valve (not shown) is provided to control the movement of the needle 22 with respect to the seat 25 at the tip of the injection nozzle 21. The control valve is operable to increase or decrease the fuel pressure in a control chamber 41 disposed at the end of the needle 22 opposite the tip 24, by controlling flow between the control chamber 41 and a low-pressure drain (not shown). The control chamber 41 is connected to the high-pressure fuel supply, so that the pressure in the control chamber 41 can be switched between the relatively high supply pressure and a relatively low pressure according to the position of the control valve. The force difference due to fuel pressure in the control chamber 41 acting in a downward direction, in combination with the spring 26, to seat the needle 22, compared with pressure in the accumulator volume 29a acting in an upward direction to unseat the needle 22, determines whether or not the needle lifts from the seat 25.
When the control valve is operated to connect the control chamber 41 to drain, the pressure of fuel in the control chamber 41 decreases, and the higher pressure of fuel in the accumulator volume 29, 29a acting on the upwardly directed surfaces of the needle causes the needle 22 to move away from the seat 25 of the nozzle body 23. This allows the fuel to be sprayed through the apertures 28 and enter the engine. When the control valve moves to close communication between the control chamber 41 and the drain, the pressure in the control chamber 41 increases back to the supply pressure, and as a result of the higher force applied to the upper end of the needle 22, the needle 22 moves back on to the seat 25 so as to seal the injection nozzle 21 and end the injection.
To ensure that the pressure difference between the fuel in the control chamber 41 and the fuel in the accumulator volume 29a is sufficient to create an adequate closing force on the needle 22 during this closing operation, as noted above a flow restriction is included between the high-pressure supply and the accumulator volume 29a. In this embodiment, the flow restriction is in the form of a restricted orifice (not shown) on the flange 43 and/or a clearance between the flange 43 and the body 23.
To prevent the collar 31 from lifting away from the conical seat 25 of the nozzle body 23, a further compression spring 35 is provided between the upper planar surface 32 of the collar 31 and a lower surface 36 of the elongate region 37 of the needle 22. Thus, when the needle 22 moves away from the conical seat 25, the compression spring 35 provides a biasing force which retains the collar 31 in position on the conical seat 25. It is noted that in an alternative embodiment the nozzle 21 may be arranged such that the collar 31 is held in contact with the seat 25 by the high pressure fuel.
Thus, the upper planar end surface 32 of the collar 31 serves to provide a suitable seat for the lower end of the compression spring 35, and the lower conical end surface 33 of the collar 31 serves to abut the conical seat 35 of the nozzle body 23 so as to perform the desired centring function. As the collar 31 remains in contact with the conical seat 25 at all times and is self-guided into central alignment by virtue of interaction of the complementary conical profiles of the seat 25 and the collar 31, expansion of the body 23 under action of high pressure fuel does not cause misalignment of the collar 31. Instead, the collar 31 contracts slightly under high pressure acting over the external surfaces of the collar 31, which does not impair its guiding function. The collar 31 therefore ensures accurate alignment of the needle 22, and does not suffer from the machining problems noted above associated with providing a guide on the needle tip 24.
As in the known injection nozzle described above with reference to Figure 1, in the embodiment of Figure 2 a voltage is applied to the valve needle 22 using an electrical input (not shown) to provide timing information, enabling improved control of the nozzle 21. Both the needle 22 and the body 23 are made from electrically conductive material, and so an electric circuit is completed when the tip 24 engages the conical seat 25. The voltage applied to the needle 22 then creates a control signal that is delivered to the engine control unit through an output (not shown). This control signal indicates the precise moment at which the valve needle 22 engages the seat 25, which is valuable data for optimising control of the nozzle in ongoing operation.
To ensure that a control signal is not generated before the needle 22 engages the seat 25, the surfaces of the proximal guiding region 30 and the flange 43 that contact the body 23 are electrically insulated to prevent creation of a conductive path for the voltage applied to the needle 22. For example, the external surfaces of the guide piece 42 and the flange 43 may be coated or covered with insulating material.
In addition, the collar 31 is of non-conductive material, for example plastics or ceramic, such that the collar 31 acts as an electrical insulator to prevent conduction of an electrical current from the needle 22 to the body 23 while the needle 22 is disengaged from the seat 25. This ensures that the control signal is only generated when the needle 22 engages the seat 25, therefore providing accurate timing data.
In this embodiment, the side surface of the lower end of the needle 22 is formed with slots or flutes 38 in order to provide one or more channels along which the fuel can pass from the accumulator volume 29a to the apertures 28. The flutes 38 provide a relatively large flow area for fuel, so that the fuel pressure downstream of the collar 31 is substantially the same as the fuel pressure upstream of the collar 31 during injection. Said another way, in this embodiment, the collar 31 causes substantially no restriction in fuel flow.
Figure 4 shows an embodiment of the collar 31 in close-up perspective view. This embodiment of the collar may be used in the nozzle shown in Figure 2, or in nozzles according to alternative embodiments. It can be seen that the collar 31 of this embodiment includes slots 39 in the lower end which serve as channels for enabling the passage of fuel from the accumulator volume 29a to the apertures 28. The elongate slots 39 thus provide the same function in this embodiment as do the slots or flutes formed in the needle as described above with reference to Figure 2. It is noted that the slots 39 of the collar can be used in addition to or instead of the slots or flutes of the needle 22 for providing a flow route for fuel.
The insulating collar 31 shown in Figure 4 provides an electrically insulating guide assembly for the needle 22 that both guides and insulates the needle 22. A second embodiment of the injection nozzle is illustrated in Figure 5 in schematic cross-section, in which the same reference numerals as in Figure 2 are used to indicate the same or equivalent features. This embodiment is substantially identical to that described above with reference to Figure 2, except that the collar 31 is not necessarily non-conductive, and may be metallic for example. This beneficially allows the collar 31 to be manufactured from standard materials such as steel, which may be cheaper than manufacturing it from, for example, ceramic material, especially in view of the manufacturing tolerances involved for ensuring accurate guiding.
To isolate the needle 22 from the body 23 prior to engagement with the seat 25, the electrically insulating guide assembly of this embodiment comprises an insulating layer 40 of non-conductive material is disposed between the needle 22 and the collar 31. The insulating layer 40 may be of any non-conductive material, for example ceramic or plastics as also used in the proximal guiding region 30. The insulating layer 40 may be implemented in the form of insulating tape.
In this embodiment, the insulating layer 40 coats at least the distal portion of the needle 22, and so slides relative to the collar 31 as the needle 22 reciprocates within the body 23. The tip 24 is left exposed to enable it to make electrical contact with the seat 25 on engagement. In other embodiments, the insulating layer 40 may be fixed to the internal surface of the collar 31.
Although preferred embodiments of the present invention have been described above, it will be apparent that numerous modifications could be made without departing from the scope of the present invention which is defined solely by the claims below. For example, although the profiling of the outer surface of the needle and the provision of slots or holes in the collar are described as alternative embodiments, these could readily be combined to provide additional channels for the fuel to pass from the chamber to the apertures.

Claims

An injection nozzle (21) for an internal combustion engine, the nozzle (21) comprising an elongate hollow body (23) and a needle (22) arranged to reciprocate within the hollow body (23) to permit fuel to be dispensed from at least one aperture (28) at a distal end (27) of the body (23), the distal end of the body (23) defining a profiled seat (25) against which the needle (22) is arranged to bear to seal the nozzle (21), characterised in that the injection nozzle (21) further comprises:
an electrically insulating guide assembly including a guide (31) which abuts the seat (25) throughout reciprocating movement of the needle (22) so as to centre the distal end (24) of the needle (22) within the body (23) as needle movement is guided, the electrically insulating guide assembly being arranged to insulate the needle (22) electrically from the body (23) when the needle (22) is disengaged from the seat (25) and,

wherein the seat (25) is substantially conical and,

wherein the guide (31) comprises a substantially conical surface (33) which abuts the seat (25).
An injection nozzle (21) as claimed in claim 1, further comprising means (35) for biasing the guide (31) towards the seat (25).
An injection nozzle (21) as claimed in claim 2, wherein the biasing means (35) comprises a compression spring (35) located between the guide (31) and a proximal end portion of the needle (22).
An injection nozzle (21) as claimed in any preceding claim, wherein the guide (31) is formed from non-conductive material, thereby to insulate the needle (22) electrically from the body (23) when the needle (22) is disengaged from the seat (25).
An injection nozzle (21) as claimed in claim 4, wherein the guide (31) is formed substantially of plastics or ceramic.
An injection nozzle (21) as claimed in any preceding claim, wherein the electrically insulating guide assembly comprises a layer (40) of non-conductive material on the surface of needle (22) and/or on the surface of the guide (31), thereby to insulate the needle (22) electrically from the body (23) when the needle (22) is disengaged from the seat (25).
An injection nozzle (21) as claimed in claim 6, wherein the layer (40) is substantially of plastics or ceramic.
An injection nozzle as claimed in any preceding claim, wherein the guide (31) comprises a generally tubular collar (31).
An injection nozzle (21) as claimed in any preceding claim, wherein the needle (22) is formed with at least one channel (38) for conveying the fuel to the at least one aperture (28).
An injection nozzle (21) as claimed in any preceding claim, wherein the guide (31) is shaped so as to define at least one channel (39) for conveying the fuel to the at least one aperture (28).
An injection nozzle (21) as claimed in any preceding claim, comprising a further guide (30) located around the proximal end of the needle (22) and arranged to centre the proximal end of the needle (22).
An injection nozzle (21) as claimed in any preceding claim, and configured such that, in use, the fuel pressure immediately upstream of the guide (31) is substantially equal to the fuel pressure immediately downstream of the guide (31).