Patent Description:
In a diesel fuel injector, the displacements of a valve member, or needle, between an open position and a closed position enable, or forbid, fuel injection through spray holes provided in the nozzle body of the injector. The needle is an elongated shaft-like member extending from a head portion, protruding in a control chamber, to a pointy extremity provided with a (moving) seating face that cooperates with a (fixed) seating face integral to the nozzle body. The needle is slidably guided in the nozzle body and, in closed position the moving seating face is in sealing contact against the fixed seating face closing fluid communication to the spray holes and thus forbidding fuel injection. In open position the moving seating face is lifted away from the fixed seating face thus opening said fluid communication and enabling fuel injection through the spray holes. <CIT> discloses such a fuel injector.

In order to comply with emissions standards, a proper operation of a fuel-injected engine requires that the fuel injectors and their controller allow for a timely, precise and reliable fuel injection, whatever the operating condition and during all injector lifecycle.

It is now known that major improvement in the control of fuel injection equipment and of the injection event is obtained with a so called closed-loop control method. <CIT>, for example, discloses a fuel injector designed with a switch function for detecting needle opening and closing. The needle is axially guided in its upper region by a guide member that is set to a predetermined electric potential. The needle is mounted in the nozzle body so as to be able to move therein while being electrically isolated from the nozzle body, except for the region of the nozzle body seat, so that the needle is in electric contact with the nozzle body only in closed position.

More generally, closed loop control methods are typically executed by an electronic control unit (ECU) that controls the operation of the fuel injection equipment and in particular the control valve of the fuel injector. Depending on embodiments, the close loop means enable for an electrical signal to be measured at a specific value when the needle gets in closed position, or the signal can also take a specific value when the needle is in fully open position. Overall, the closed loop detection functions permits determining the opening time, and thus estimating the injected fuel quantity which is dependent on needle opening time and fuel pressure.

It has been observed that certain operating conditions may cause an erroneous detection of the needle opening. During early opening of the needle (i.e. within the first few microns of lift), cavitation may appear between the needle and the nozzle seat, leading to a hesitating electrical contact. Sometimes, the distance between the needle tip and valve seat is sufficient to open the electric link. Sometimes the distance is insufficient and the electric link remains closed due to the electric field. Still another possibility is that the needle tip deviates from its axis to be in contact with the seat, so that the electric link is closed. These phenomena are thus at the origin of an unstable switching signal.

The object of the present invention is to provide a fuel injector of improved design, wherein a stable closed loop detection signal is ensured.

This object is achieved by a fuel injector as claimed in claim <NUM>.

According to the present invention, a nozzle assembly for a fuel injector comprises a nozzle with a body extending along a main axis, the body having a peripheral wall and defining an internal bore in which a needle is axially moveable between a closed position, in which a first end of the needle rests on a valve seat to prevent fuel injection through one or more injection orifices of the nozzle, and an open position in which the needle is lifted from its seat to allow injection.

The needle extends along a needle axis (A) and has an overall shape with symmetry of revolution about the needle axis (A), the needle comprising a shaft portion which is tapered at the first end and defines an annular seating face cooperating with a seating face on the valve seat.

The needle assembly further includes a detection circuit in which the needle forms a switch.

It shall be appreciated that the needle is designed to include a local dissymmetry in the region of the annular seating face, which is configured to cause, in use, an unbalance of forces resulting in a transversal force exerted by the fuel about the needle's first end.

The local dissymmetry will come in play at the beginning of the needle opening stroke. During the first microns of needle lift, the needle tip is still in the vicinity of the nozzle seating face and will be pushed transversally/radially (in a given direction) due to the imbalance of forces. The needle tip will thus remain in contact with the nozzle seating face until the needle stroke is sufficient. That is, the needle tip is forced, by the design of the dissymmetry, to remain in contact with the nozzle seating face. A clean electric contact can thus be obtained and the opening time can be more reliably detected.

As used herein, the term "symmetry of revolution" is used in its conventional meaning, and is equivalent to "circular symmetry". The needle axis is thus an axis of revolution of the needle.

Advantageously, the tapering first end includes an intermediate section connected at one end to the needle shaft portion and the other end to a conical section defining the annular seating face. The conical section is generally the very end section of the needle. Although referred to as conical section, it may be truncated, i.e. without the apex. In embodiments, the conical section may include two or more sections with different cone angles.

The conical section includes the needle seating face and is configured to define a contact line, which is the line along which the sealing contact will form against the nozzle seating face in closed position.

The contact line lies in a plane substantially perpendicular to the needle axis (A) and the local dissymmetry is adjacent the contact line. The local dissymmetry may be provided above and/or below the contact line, but does not cross the contact line. When there are two local dissymmetries, they may be angularly aligned.

Preferably, the local dissymmetry is adjacent the contact line, on the side of the intermediate section. The local dissymmetry may extend to the intermediate section.

The conical section has circular symmetry about the needle axis (A) except over a predetermined angular section that is less than <NUM>°. Preferably, the predetermined angular section is in the range of <NUM> to <NUM>°, in particular <NUM> to <NUM>°.

The local dissymmetry is formed by a truncated peripheral portion of the conical section, for example removed by machining.

In this embodiment, the local dissymmetry is thus designed as an interruption of the outer circumference of the conical section. The conical section has a symmetrical cross-section profile (in particular circular symmetry), but the local dissymmetry interrupts that symmetry, resulting in an unbalanced cross-section.

The needle shaft generally has a symmetry of revolution about axis (A). It may comprise one or more collar members that have a symmetry of revolution about axis or about a plane passing through axis.

In the first embodiment, the term "local dissymmetry" only concerns a part of the circumference of the conical section. However the local dissymmetry may extend to the whole first end of the needle. Compared to the needle axial extent, it can still be called "local".

In this context, in a second embodiment, the conical section is configured to define a contact line in a plane tilted with respect to the needle axis (A) and the outer shape of the tapered tip is defined, above the contact line, by a generatrix parallel to the needle axis and following the contact line.

In a third embodiment, the intermediate section and the conical section have an axis of symmetry referred to as tip axis (B) that is parallel to the needle axis (A) and offset therefrom. The intermediate section and the conical section have circular symmetry about the tip axis.

According to another aspect, the invention concerns a fuel injector for an internal combustion engine comprising the herein disclosed nozzle assembly.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:.

In reference to <FIG> is now described a diesel fuel injector <NUM> having a general elongated shape extending along a main axis A and comprising, from bottom to top, a nozzle assembly <NUM>, a control valve assembly <NUM> and an actuator assembly <NUM>. These assemblies are fixed to each other via a capnut <NUM>. The details of the actuator assembly <NUM> and control valve assembly <NUM> are known in the art and are not shown in the figures, being simply indicated by boxes.

The injector <NUM> defines an internal high pressure fuel circuit <NUM> comprising several segments and extending from an inlet section <NUM> provided in the upper part of the injector to spray holes <NUM> arranged in a lower spray extremity <NUM> drawn at the very bottom of the injector <NUM>.

The nozzle assembly <NUM> comprises a nozzle body <NUM> having a peripheral wall <NUM> defining an inner bore <NUM> in which is slideably arranged a needle <NUM>, forming the valve member, and adapted to translate along the main axis A between a closed position CP and an open position OP.

The needle valve member <NUM> has an elongated shaft core <NUM> extending (along needle axis concentric with axis A) between a top head end <NUM> and a lower end with a tapered tip <NUM>. In between the ends, the needle <NUM> is provided with a radially protruding collar member <NUM> that extends toward a circular edge that lies close to the inner face of the inner bore <NUM> of the nozzle body <NUM>. The collar member <NUM> divides the inner bore <NUM> into an upstream chamber <NUM> and a downstream chamber <NUM> and, a permanently open fluid communication is defined between these chambers by at least one restricted aperture provided in the collar member <NUM>, or at the periphery of it or, along the circular edge. Reference sign <NUM> designates a guide collar similar to collar member <NUM> to guide the needle <NUM> in the lower region of bore <NUM>.

The spray extremity <NUM> is the arrangement of the tapered end <NUM> of the needle defining a male needle seating face <NUM> cooperating with a corresponding female nozzle seating face <NUM> defined on the inner face of the nozzle body <NUM>. The needle seating face <NUM> is also said to be mobile because it moves with the needle, whereas the nozzle seating face <NUM> is referred to as fixed seating face. In the spray extremity <NUM>, the inner bore <NUM> that is cylindrical, downwardly narrows forming said female nozzle seating face <NUM> ending in a small sac <NUM> wherefrom depart the spray holes <NUM> extending through the peripheral wall <NUM> of the nozzle body <NUM>.

As is known in the art, in the closed position (CP) of the needle <NUM> - illustrated in <FIG>- the male seating face <NUM> rests sealingly on the female seating face <NUM> and fuel flow towards the spray orifices <NUM> is prevented. An opening position (OP) of the needle <NUM> is a position where the needle <NUM> is off the valve seat, i.e. there is a space between the male seating face <NUM> and female seating face <NUM>, whereby fuel can flow through this space downstream of the valve seat to the spray orifices <NUM>, so that fuel is sprayed at the injector tip into the combustion chamber.

Actuation of the needle <NUM> is performed by energizing the actuator assembly <NUM>, typically a solenoid that acts on a valve member of the control valve assembly <NUM>. The control valve assembly <NUM> is conventionally connected with a control chamber <NUM> at the top of the nozzle assembly <NUM>, in which the needle head <NUM> (opposite tip <NUM>) protrudes. Energizing the actuator <NUM> will thus cause triggering of the control valve (connected to a mobile armature of the solenoid actuator) that will open an escape path for fuel out of control chamber <NUM>. This will cause a decrease of pressure in the control chamber <NUM>, whereby needle <NUM> will move upward into the control chamber in OP and thus open the valve seat. This principle of operation is well known.

Fuel injector <NUM> further comprises a detection circuit for detecting needle opening and closing, which is also referred to as closed loop. In the present embodiment, this is achieved by a simple switch function. The needle <NUM> is axially guided in its upper region by a guide member <NUM> that is set to a predetermined electric potential. The guide member <NUM> has an axial bore in which the needle head <NUM> is received. The needle <NUM> is mounted in the nozzle body <NUM> so as to be able to move therein while being electrically isolated from the nozzle body <NUM>, except for the region of the nozzle body seat <NUM>, so that the needle <NUM> is in electric contact with the nozzle body <NUM> only in CP. The needle <NUM> is electrically insulated from the body <NUM> by means of insulating sheeting or coatings indicated <NUM> provided at the collars <NUM>, <NUM> and at the interface with the guide member <NUM>.

When the needle is in CP, the circuit is closed and an electric current can flow from the upper guide <NUM> through the length of the needle <NUM> to pass into the body <NUM> at the needle tip in contact with the female seating face <NUM>. This detection circuit and flow path is indicated by line <NUM> in <FIG>. When the needle <NUM> is in OP, the detection circuit is open and no current can flow to the body <NUM>. There, in CP the voltage may thus be <NUM> V whereas in OP the circuit is open a predetermined voltage, e.g. <NUM> V, is measured. This is only one way of performing closed loop detection and a variety of voltages and designs may be used, e.g. including detection of the fully open needle position, as will be clear to those skilled in the art.

In order to ensure a clean electric contact at opening or closing of the needle <NUM>, the needle <NUM> is designed to include a local dissymmetry in the region above the male seating face <NUM>. The local dissymmetry is configured to cause, in use, a transversal force exerted by the fuel in the region of the needle tip <NUM>.

The needle tip <NUM> is shown in more details at <FIG>. It may be noted that a general rule of design of an injector needle is to have an overall symmetrical shape in order to maintain balance of the opening forces and to avoid lateral forces applied to the needle. This is the case in the present embodiment and the needle <NUM> has an overall symmetrical shape. In particular the core shaft <NUM> exhibits a symmetry of revolution (i.e. circular symmetry) about the needle axis A. Depending on the embodiments, this may also be the case for the annular collars <NUM>, <NUM>. In other embodiments, as is the case here, the collar members <NUM> and <NUM> may not have an axial symmetry but a symmetry with respect to a plane passing through the needle axis A, still chosen to maintain a proper balance of forces.

It will be noticed that at the lower end of needle <NUM>, the core shaft <NUM> terminates with the tapering end <NUM> which comprises an intermediate section <NUM> followed by a conical section <NUM>.

The intermediate section <NUM> and conical section <NUM> generally have circular symmetry about axis A, except for a certain portion of the periphery at <NUM> that is modified to provide a local dissymmetry configured to cause, in use, a transversal force (in a given direction) exerted by the fuel about the needle tip <NUM>.

In this first embodiment, the local dissymmetry <NUM> is obtained by machining (milling or grinding) a part of the outer periphery of the conical section <NUM>. The conical section <NUM> is initially a cone, or more precisely a cone with truncated apex, and the milling thus results in an interruption of the axial symmetry of the conical section <NUM>.

In other words, the conical section <NUM> has a symmetry of revolution about axis A (i.e. a circular cross-section) except over a predetermined angular section that may be generally in the range of <NUM>° to <NUM>°.

As is known, although the male and female seating faces <NUM> and <NUM> have a certain axial extent, in the CP the configuration is such that there is a continuous, circumferential contact line that forms the actual sealing contact between the seating faces. In <FIG> the contact line on the male seating face <NUM> is represented by dashed line <NUM>.

It may be noted that the local dissymmetry is provided on the male seating face <NUM> of the needle <NUM>, above the contact line <NUM> (adjacent thereto on the side of the intermediate section <NUM>). When the needle is in CP, this local dissymmetry does not have any effect. However, the local dissymmetry causes, at opening, an unbalance of forces on the needle tip that results in a transversal/radial force. This will impact the injector operation at the very beginning of the needle opening, i.e. within the first microns of the lift-off stroke. Due to the transversal forces, the needle is pushed on the side and remains in contact with the female seating face.

This design thus promotes the contact between the needle tip <NUM>, precisely the conical section <NUM>, and the female seating face <NUM>, thereby avoiding oscillations or random needle behavior that may be observed under certain conditions. The needle tip <NUM> is forced to remain in contact with the female seat <NUM> until it has been sufficiently lifted. Accordingly, the seat detection circuit remains closed during this initial period, leading to a stable electric signal.

It may be noted that the local dissymmetry may extend into the the intermediate section <NUM>, as seen in <FIG>. This is due here to the use of the grinding tool that attacks the conical section <NUM> parallel to axis A.

In embodiments, the conical tip <NUM> may comprise several conical sections along axis A with different angles. This is e.g. the case in this embodiment where the cone angle of the section downstream (on the right) of the contact line <NUM> is larger than the upstream one (on the left).

In some embodiments, the conical section <NUM> may also be configured with a local dissymmetry in the region below of the contact line <NUM> (towards the free end). Such dissymmetry should correspond angularly to the one above the contact line <NUM>. The additional dissymmetry will promote flow on one side of the needle at opening and hence increase the transversal force on the needle.

The local dissymmetry is here obtained by an interruption in the circular outer shape of the conical section, over a minor part of the circumference. The needle being typically made in one piece, it is a solid of revolution and the dissymmetry is obtained here by removing material at one location of the periphery. The aim is to modify the outer shape of the intermediate section to cause an unbalance of forces that pushes the needle in one direction. In general the intermediate section will thus have, over at least part of its length, a circular cross-section except at the position of the removed material <NUM> at the tip, preferably just above contact line <NUM>.

Those skilled in the art may devise other shapes to generate a transverse force at the needle tip. Cross-sections differing from a circle but retaining some symmetry and thus keeping force balance such as e.g. strict elliptical or polygonal shapes are thus to be avoided, unless they are modified with a flattened portion as described above.

Two further embodiments are represented in <FIG>, and will be explained with comparison to <FIG>, which illustrates the conventional needle design. In <FIG> one will recognize a conventional needle <NUM> having a shaft core <NUM> with tapering end <NUM> extending along a main axis A. The tapering end includes an intermediate section <NUM> extending between the core end and a conical section <NUM>. The needle has a symmetry of revolution about axis A. Intermediate section <NUM> and conical section <NUM> are also symmetrical about axis A; they have a strictly circular cross-section in a plane perpendicular to axis A, this over their entire axial extent.

In the embodiment of <FIG>, the needle <NUM> has a core <NUM> with a symmetry of revolution about axis A. This is however not the case for the intermediate section <NUM>. In fact, in this embodiment the seat line <NUM> is configured to be tilted relative to the needle axis A. The outer shape of the tapering end <NUM> is made, above the seat line, based on a generatrix parallel to axis A and following the seat line <NUM> (which thus forms the directrix). The region of the conical section <NUM> is thus symmetrical below the seat line, with a circular cross-section. However the transition section does not have a circular cross-section. In the view from below the dotted circle represents the cross-section of a circular intermediate section as in <FIG>. Here however the design of a needle tip <NUM> results in an dissymmetric intermediate section <NUM>. The dashed surface <NUM> represents the removed portion compared to a circular design.

Compared to the embodiment of <FIG>, there is more horizontal surface on the right of intermediate section <NUM> (i.e. the surface <NUM>) and a larger vertical surface on the right as well. This leads to an imbalance of forces acting on the needle <NUM> that will push the needle tip <NUM> to the left, as indicated by the arrow in Fig.<NUM> a).

In the embodiment of <FIG>, the tapering end <NUM> has been offset from the main axis A of needle <NUM>. The shaft core <NUM> has a symmetry of revolution about axis A. The intermediate section <NUM> and conical section <NUM> have a symmetry of revolution about an axis B parallel to axis A but offset therefrom.

Claim 1:
A nozzle assembly of a fuel injector comprising:
a nozzle (<NUM>) with a body (<NUM>) extending along a main axis, said body having a peripheral wall (<NUM>) and defining an internal bore (<NUM>) in which a needle (<NUM>) is axially moveable between a closed position, in which a first end (<NUM>) of said needle rests on a valve seat to prevent fuel injection through one or more injection orifices (<NUM>) of said nozzle, and an open position in which said needle is lifted from said seat to allow injection;
wherein said needle extends along a needle axis (A) and has an overall shape with symmetry of revolution about said needle axis (A), said needle comprising a shaft portion (<NUM>) which is tapered at said first end (<NUM>) and defines an annular seating face (<NUM>) cooperating with a seating face (<NUM>) on said valve seat;
wherein said nozzle assembly further includes a detection circuit in which said needle forms a switch;
wherein said needle is designed to include a local dissymmetry (<NUM>) in the region of said annular seating face (<NUM>), which is configured to cause, in use, an unbalance of forces resulting in a transversal force exerted by the fuel about said needle first end (<NUM>) and, wherein said tapering first end includes an intermediate section (<NUM>) connected at one end to said needle shaft portion (<NUM>) and at the other end to a conical section (<NUM>) defining said annular seating face (<NUM>),
wherein said conical section (<NUM>) is configured to define a contact line (<NUM>) in a plane substantially perpendicular to said needle axis (A),
characterized in that said local dissymmetry (<NUM>) is located adjacent said contact line, on the side of said intermediate section (<NUM>),
wherein said conical section (<NUM>) has circular symmetry about said needle axis (A) except over a predetermined angular section that is less than <NUM>° and,
wherein said local dissymmetry is formed by a truncated peripheral portion of said conical section, for example removed by machining.