Fuel injector

Abstract

A fuel injector includes a housing extending along an injector axis. A pintle has an axially extending pintle shaft and a radially projecting annular collar with a collar surface, the pintle being axially moveable between an open position and a closed position. An armature is axially guided in the housing between a proximal position and a distal position, the armature having an axial through-hole in which the pintle shaft is guided and an armature surface which engages the collar surface, thereby moving the pintle into the open position when the armature moves to the proximal position. A first resilient member biases the pintle in the distal direction and a second resilient member biases the armature in the distal direction. The armature surface and the collar surface are slanted with respect to the injector axis and one of the armature surface and the collar surface is convex curved.

Claims

1. A fuel injector comprising: a housing extending axially along an injector axis from a proximal end to a distal end and having a nozzle at the distal end, said nozzle ending by a nozzle tip from which fuel is sprayed; a pintle having a pintle shaft which extends axially and also having an annular collar which projects radially from the pintle shaft, said annular collar having a collar surface, the pintle being axially movable between an open position and a closed position, thereby controlling flow of fuel at said nozzle tip; and an armature that is axially guided in the housing between a proximal position and a distal position, the armature having an axial through-hole therein in which the pintle shaft is guided and an armature surface which engages the collar surface, thereby transferring an axial force which moves the pintle into the open position when the armature moves to the proximal position; the armature further including a plurality of fuel channels that are disposed radially outside with respect to the through-hole; wherein a first resilient member is provided which biases the pintle toward the distal end; wherein a second resilient member is provided which biases the armature toward the distal end; wherein the armature surface and the collar surface are slanted with respect to the injector axis; and wherein the collar surface and the armature surface that engages the collar surface are both convex curved such that the collar surface has an arcuate protrusion that arcuately protrudes outwardly, the armature surface has an arcuate protrusion that arcuately protrudes outwardly, wherein the arcuate protrusion of the collar surface and the arcuate protrusion of the armature surface are spherical such that each corresponds to a portion of a surface of a sphere, wherein the arcuate protrusion of the armature surface extends from the through-hole to the fuel channels, and wherein the arcuate protrusion of the armature surface and the arcuate protrusion of the collar surface engage one another.

2. The fuel injector according to claim 1, wherein the first resilient member is a first spring bearing at one end on the annular collar and disposed on a side of the annular collar which faces toward the proximal end.

3. The fuel injector according to claim 2, wherein the second resilient member is a second spring bearing at one end on the armature and disposed a side of the armature which faces toward the proximal end.

4. The fuel injector according to claim 3, wherein the first spring and the second spring are concentrically arranged and bear, at their respective opposite ends, on respective fixed injector parts.

5. The fuel injector according to claim 1, wherein, in the closed position, an annular gap separates the armature surface and the collar surface.

6. The fuel injector according to claim 1, wherein the collar surface is spherical.

7. The fuel injector according to claim 1, wherein at least one of the collar surface and the armature surface extends annularly along a tangential direction.

8. The fuel injector according to claim 1, wherein the armature surface is disposed at a proximal end of the through-hole.

9. The fuel injector according to claim 1, wherein an axial length of the through-hole is less than 200% of its diameter.

10. The fuel injector according to claim 1, wherein the armature comprises a circumferential flange that extends distally along the injector axis and has a first armature stop surface that engages a stop surface in the housing when the armature is moved toward the distal end; and/or the armature comprises a second armature stop surface that engages a pole stop surface of the pole piece when the armature is moved toward the proximal position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a cross-sectional view of a first embodiment of an inventive fuel injector;

(3) FIG. 2 is a detail view of the pintle-armature interface of FIG. 1, during opening of the injector;

(4) FIG. 3 is a detail view of the pintle-armature interface according to a second embodiment of an inventive fuel injector; and

(5) FIG. 4 is a detail view of the pintle-armature interface according to a third embodiment of an inventive fuel injector;

(6) FIG. 5 is a detail view showing the pintle-armature interface in closed position for the injector of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

(7) In the following description, the terms above, below, upper, lower, horizontal, vertical are not only used (in a non-limiting way) with reference to the orientation of the drawings, but also in consideration to the usual understanding of those skilled in the art.

(8) FIG. 1 schematically shows an inventive fuel injector 1, which can be used in an internal combustion engine. The fuel injector 1 comprises a housing 2 consisting of several parts which are not explained here in detail. The housing 1 extends along an injector axis A from a proximal end 2.1 (i.e. upper end) to a distal end 2.2 (i.e. lower end), where a nozzle 4 ends with a tip 4.2. A cavity 8 is formed inside the housing 1, which extends along the nozzle 4 and is adapted for guiding fuel through the fuel injector 1.

(9) A pintle 10 is disposed within the housing 2, and specifically within a nozzle body 4.3, in order to control the spraying of fuel at the distal, nozzle tip 4.2. The pintle 10 has an axially extending, elongate pintle shaft 10.1, from which an annular collar 10.2 projects radially. The annular collar 10.2, which may also be referred to as pintle perch, forms a protruding stop member that is here in one piece with the pintle shaft 10.1, but could alternatively be a separate piece fixed thereto.

(10) The pintle 10 is axially movable between an open position (not shown) and a closed position, which is represented in FIG. 1. In the closed position, a ball 11 at a distal end of the pintle 10 rests against a nozzle seat 4.1 of the nozzle 4, whereby the nozzle 4 is closed. The nozzle seat 4.1 is located at the nozzle tip 4.2, upstream from one or more flow orifices 4.4. If the pintle 10 moves proximally towards the open position, the ball 11 is lifted away from the nozzle seat 4.1, whereby the nozzle 4 is opened. A first spring 6 is disposed between the housing and the pintle collar 10.2. It is a coil spring that is aligned along the injector axis A and exerts a force to distally bias the pintle 10, i.e. to bias the pintle 10 in a distal direction (onto the nozzle seat 4.1).

(11) Above the pintle 10, at the proximal end 2.1, one will recognize the actuator assembly that is only partially shown. Contained inside the housing, actuator assembly includes an annular pole piece 3 coaxially arranged with respect to axis A and surrounding the proximal pintle end, and a coil 5 surrounding the pole piece 3. Fuel is introduced in the injector at the proximal end 2.1 and flows through the actuator assembly into cavity 8 down to the nozzle tip region.

(12) The fuel injector 1 further comprises an armature 12 that has a roughly annular shape and surrounds the pintle 10. The armature 12 has an axial, central through-hole 12.1 in which the pintle shaft 10.1 is guided, i.e. the pintle shaft 10.1 can move axially in the through-hole 12.1, but radial movement with respect to the armature 12 is greatly limited. The inner cross-section of the through-hole 12.1 is adapted to the outer cross-section of the pintle shaft 10.1, both of which are circular. Radially outside with respect to the through-hole 12.1, the armature 12 comprises a plurality of fuel channels 12.6 that communicate with the cavity 8 in order to allow passage of fuel through the armature 12. The armature 12 is arranged in the nozzle body 4.3 in a cylindrical bore 4.5. The armature 12 is further axially guided in the nozzle body 4.3 between a first, proximal position and a second, distal position. In the distal position, which is shown in FIG. 1, a first armature stop surface 12.4 rests against a bottom shoulder forming a stop surface 2.3 in the nozzle body 4.3. In the present case, the stop surface 2.3 is in fact the upper surface of a non-magnetic ring 2.4 that is disposed on the bottom of cylindrical bore 4.5; such ring is conventionally provided to avoid magnetic sticking of the armature. The first armature stop surface 12.4 is disposed at a distal rim of an annular flange 12.3 of the armature 12 that extends distally parallel to the injector axis A.

(13) In the proximal position of the armature 12, which is not shown in the figures, a second armature stop surface 12.5 on a proximal side of the armature 12 engages a pole surface 3.1 of the pole piece 3. As is known, the pole piece 3 is adapted to enhance and/or shape a magnetic field that is generated by the magnetic coil 5. If a current flows through the magnetic coil 5, a magnetic field is generated and enhanced by the pole piece 3, whereby the armature 12 is pulled towards the pole piece 3 into the proximal position. A second spring 7 is disposed between the housing 2, or more specifically, the pole piece 3, and the armature 12 to distally bias (downwardly) the armature 12. As long as no magnetic field is acting on the armature 12, it is kept in the distal position by the second spring 7.

(14) The armature also comprises an armature surface 12.2 that is adapted to engage a collar surface 10.3 of the pintle collar 10.2. The armature surface 12.2, which is disposed at a proximal end of the through-hole 12.1, is adapted to transfer an axial force to move the pintle 10 into the open position when the armature 12 moves to the proximal position. In other words, the pintle 10 is moved by the armature 12, which in turn is moved by the magnetic field, wherein the force between the armature 12 and the pintle 10 is transferred via the armature surface 12.2 and the collar surface 10.3. Normally, the pintle 10 is moved by a combination of the force exerted by the armature 12 and pressure exerted by fuel in the fuel injector 1. In the embodiment shown in FIGS. 1, 2 and 5, both the armature surface 12.2 and the collar surface 10.3 extend annularly along a tangential direction and are slantedi.e. neither parallel nor perpendicularwith respect to the injector axis A. More specifically, the collar surface 10.3 is spherical and the armature surface 12.2 is conical.

(15) It may be noted that in the closed position, corresponding to FIGS. 1 and 5, the armature surface 12.2 and the collar surface 10.3 are not in contact; they are spaced by an annular gap 15. As indicated above, in the closed position the armature 12 rests on the non-magnetic ring 2.4. The armature is biased in this closed position by spring 7. Likewise, the pintle is biased in closed position by spring 6 (so that the pintle tip or ball 11 rests on the nozzle seat 4.1). The injector is configured so that in the closed position, there is an axial spacing between the pintle collar 10.2 and the armature 12 resting on ring 2.4. This axial spacing results in the annular gap 15 separating the facing armature surface 12.2 and the collar surface 10.3, as can be observed in FIG. 5. In the present embodiment, the length of the axial spacing, respectively annular gap, can be adjusted during injector assembly, in particular by adjusting the position of the nozzle tip part 4.6 comprising the seat 4.1. As can be seen, the nozzle tip is a separate part fitted at the distal end of the nozzle body. Once the nozzle tip 4.6 has been inserted in the nozzle body 4.3 to the desired depth, to control the desired annular gap 15, the nozzle tip 4.6 is welded.

(16) The present configuration is advantageous in that it limits the pintle/armature contact and hence reduces wear of the cooperating surfaces. When injector coil 5 is energized, the armature 12 takes off and moves upward alone over the distance of the axial spacing, and then impacts the pintle collar 10.2, whereby both the armature 12 and pintle 10 move upward. The armature's proximal displacement is limited by the pole piece 3. The impact of the armature 12 into the pintle collar 10.2 forces the pintle to open. The pintle 10 tends to undergo an overshoot but is brought back against the armature 12 by spring 6 in the open position, as long as the coil 5 is energized. The contact/pintle remains during the needle closing stroke. This because the armature 12 sees mechanical and hydraulic friction, but also because there is still some magnetic attraction towards the pole piece 3. Once the pintle 10 with ball 11 are contacting the seat 4.1, the armature 12 detaches from the pintle 10 and travels alone to the stop ring 2.4. The biasing spring 7 assists in pushing the armature towards the stop ring 2.4 and minimizes the number of bounces. Back in closed position, the armature and pintle collar are separated by annular gap 15. It should be observed here that thanks to the present configuration, the armature surface 12.2 and the collar surface 10.3 are in contact essentially during an injection event, but not in closed position. Taking into consideration the operation of an internal combustion engine, and having in particular regard to combustion cycles, it is estimated that the armature and pintle are in contact about 1 to 5% of the time. This hence limits contact, and thus wear, at contact surfaces, which is favorable for enhanced injector lifetime.

(17) An axial length of the through-hole 12.1 is less than its diameter, i.e. the through-hole 12.1 is comparatively short, wherefore the pintle 10 is not stabilised against tilting with respect to the injector axis A as much as with a longer through-hole. However, even if some tilting or misalignment between the pintle 10 and the armature 12 occurs, the shape of the armature surface 12.2 and the collar surface 10.3 enable the pintle collar 10.2 to always stay in contact during opening with the armature surface 12.2 along an annular contact area 13 (see FIG. 2). Effectively, the collar surface 10.3 and the armature surface 12.2 can be considered as forming a ball link. Since the contact area 13 is always annular (as opposed to point-shaped, i.e. one-dimensional), the local stress and abrasion can be limited, thereby prolonging the service lifetime of the fuel injector 1.

(18) Thinking in terms of degrees of freedom, one can say that in the distal (closed) position the armature has following constraints: Axial position frozen, by injector body stop surface and biasing spring pushing; Horizontal orientation frozen, by injector body stop surface and biasing spring pushing; Horizontal position frozen, by contact armature outer diameter and injector body inner diameter; Rotation around central axis A is possible.

(19) Once the armature has left the stop surface 2.3, it has following constraints: Axial position: free=movement; Horizontal position and horizontal orientation frozen by contact between the armature outer diameter and the injector body internal diameter; Rotation around central axis possible.

(20) When the armature is in contact with the pintle, the armature is free in axial direction (movement), its horizontal position and horizontal orientation are frozen by the contact between the armature outer diameter and the injector body inner diameter; the rotation around central axis A is possible. For the pintle, the axial position and horizontal position are frozen, by contact between the pintle sphere to armature cone and core spring pushing; the rotation around central axis A is possible, the horizontal orientation is free.

(21) FIG. 3 shows a detailed view of a second embodiment, which is largely identical to the first embodiment shown in FIGS. 1 and 2. In this embodiment, however, the collar surface 10.3 is also convex curved, while the armature surface 12.2 is concave curved with a curvature that is less than the curvature of the collar surface 10.3. As compared to the first embodiment, the cooperation of the convex curved and the concave curved surface may help to increase the contact area 13, thereby further limiting local stress.

(22) FIG. 4 is a detail view of a third embodiment, in which both the collar surface 10.3 and the armature surface 12.2 are convex curved.