Fluid injector

Abstract

A fluid injector for a combustion engine has a tubular body which hydraulically connects a fluid inlet end of the injector to a fluid outlet end of the injector. A magnetic core is affixed inside the body, a solenoid is disposed on the outside of the body, and an axially moveable armature is disposed inside the body. A valve assembly controls an axial flow of fluid through the body. The valve assembly has a valve needle to be operated by the armature and a sleeve of diamagnetic material which is located radially between the armature and the body.

Claims

1. A fluid injector for injecting fuel into a combustion engine, the fluid injector comprising: a tubular body hydraulically connecting a fluid inlet end of the injector to a fluid outlet end of the injector; a magnetic core affixed inside said body; a solenoid disposed on an outside of said body; an armature inside said body and mounted for axial movement; a valve assembly for controlling an axial flow of fluid through said body, said valve assembly including a valve needle configured to be operated by said armature; said valve needle including an armature retainer formed for extending into a corresponding cavity formed in said magnetic core and for axially guiding said valve needle; said valve needle extending axially through said armature and said armature retainer being shaped for permitting a predetermined tilting of said valve needle with respect to said magnetic core; and a sleeve of diamagnetic material disposed radially between said armature and said body, said sleeve being affixed to an inner radial surface of said tubular body and said tubular body, said sleeve and said armature being dimensioned for forming an annular gap between said sleeve and said armature, said sleeve having a mass and a magnetic susceptibility selected for substantially cancelling out radial forces on said armature with radial forces from said sleeve when said solenoid is energized; said armature and said sleeve overlapping axially and said sleeve being operable for generating an increasing force biasing said armature away from said tubular body the closer said armature comes to said tubular body.

2. The injector according to claim 1, wherein said annular gap is a fluid-filled gap.

3. The injector according to claim 1, wherein said sleeve comprises a polymer having a diamagnetic material suspended therein.

4. The injector according to claim 1, wherein said valve needle is a tube extending axially through said armature for conducting the fluid.

5. A fluid injector for injecting fuel into a combustion engine, the fluid injector comprising: a tubular body hydraulically connecting a fluid inlet end of the injector to a fluid outlet end of the injector; a magnetic core affixed inside said body; a solenoid disposed on an outside of said body; an armature inside said body and mounted for axial movement; a valve assembly for controlling an axial flow of fluid through said body, said valve assembly including a valve needle configured to be operated by said armature; said valve needle including an armature retainer formed for extending into a corresponding cavity formed in said magnetic core and for axially guiding said valve needle; said valve needle extending axially through said armature and said armature retainer being shaped for permitting a predetermined tilting of said armature with respect to said magnetic core; and a sleeve of diamagnetic material disposed radially between said armature and said body, said sleeve being affixed to an inner radial surface of said tubular body and said tubular body, said sleeve and said armature being dimensioned for forming an annular gap between said sleeve and said armature, said sleeve having a mass and a magnetic susceptibility selected for substantially cancelling out radial forces on said armature with radial forces from said sleeve when said solenoid is energized; said armature and said sleeve overlapping axially and said sleeve being operable for generating an increasing force biasing said armature away from said tubular body the closer said armature comes to said tubular body.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) An exemplary embodiment of the fluid injector will now be described in more detail with reference to the figures, in which:

(2) FIG. 1 shows a longitudinal section view of a portion of a fluid injector according to an embodiment;

(3) FIG. 2 shows a magnification of a part of the fluid injector of FIG. 1, and

(4) FIG. 3 shows a schematic diagram of energy levels of the armatures of different fluid injectors.

DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows a longitudinal section of a fluid injector according to an embodiment of the invention. The fluid injector is configured for controlling a flow of fuel into an internal combustion engine, especially a piston engine for use in a motor vehicle. In other words, the fluid injector of the present embodiment is a fuel injector 100 for an internal combustion engine. It is in particular provided for dosing fuel directly into the combustion chamber of the internal combustion engine.

(6) The fuel injector 100 comprises a tubular body 105 that extends along a longitudinal axis 110 for hydraulically connecting a fluid inlet end of the injector 100 to a fluid outlet end of the injector.

(7) The fuel injector 100 comprises an actuator assembly comprising a coil which is in particular in the shape of a solenoid 115, a magnetic core 120 and a moveable armature 125. The solenoid 115 is arranged radially subsequent to the tubular body 105 on the outside of the tubular body 105. The solenoid generally comprises a number of turns wound around the longitudinal axis 110. The solenoid 115 may be affixed to the outside of the body 105. The magnetic core 120 is arranged inside the body 105 so that it faces the solenoid 115. The core 120 is magnetici.e. in particular it is made from a magnetic material such as a ferromagnetic material, for example from a ferritic steeland, thus, may help channelling or controlling the magnetic field which is generated when the solenoid 115 is energized by supplying an electrical current that flows through the turns of the solenoid 115. The armature is arranged inside the tubular body 105 axially adjacent to the magnetic core 120 and in particular downstream of the magnetic core 120. The armature 125 is axially displaceable in reciprocating fashion along the longitudinal axis 110 with respect to the tubular body 105 and the magnetic core 120 which is positionally fix with respect to the latter. The armature 125 is also made of a magnetic material such as a ferritic steel so that it will be attracted by the magnetic core 120 when the solenoid 115 creates a magnetic field.

(8) The fuel injector further comprises a valve assembly 130. The valve assembly 130 comprises a valve needle 135. Expediently, it further comprises a valve seat (not shown in the figures) which cooperates with the valve needle to prevent fluid flow from the fluid injector in a closing position of the valve needle 135 and enables dispensing of fluid from the fluid injector through one or more injection holes in further positions of the valve needle. Such a valve assembly is also useful for any other embodiment of the fluid injector.

(9) The armature 125 is connected to a valve assembly 130 via the valve needle 135. In particular, the armature 125 is mechanically coupled to the valve needle so that it is operable to displace the valve needle 135 away from the closing position. It is preferred that the valve needle 135 is hollow such as to permit a flow of fuel parallel to the longitudinal axis 110 towards the valve assembly 130. The valve needle 135 may especially include a tube that runs axially through the armature 125.

(10) In the present exemplary embodiment, the armature 125 is axially displaceable with respect to the valve needle 135. Relative axial displacement of the armature 125 and the valve needle 135 is limited by an armature retainer 140 which is comprised by the valve needle 135. The armature retainer 140 may be fixed to the tubular shaft of the valve needle 135 as in the present embodiment. Alternatively, the armature retainer 140 may be in one piece with the shaft of the valve needle. By means of interaction with the armature retainer 140, the armature 125 is operable to take the valve needle 135 with it when moving in axial direction towards the magnetic core 120.

(11) The armature retainer 140 extends into a corresponding cavity 145 of the magnetic core 120 in the present embodiment. The member 140 will be discussed in more detail below with respect to FIG. 2.

(12) It is furthermore preferred that a first elastic member 150 is configured to press the valve needle 135 in a direction away from the core 120, which is in particular equivalent with an axial direction towards the valve seat. In other words, the first elastic member 150 is configured to bias the valve needle 135 towards the closing position. By means of mechanical interaction via the armature retainer 140, the armature 125 is also biased in axial direction away from the magnetic core 120 by the first elastic member 150. Thus, the armature 125 may move away from the core 120 when the solenoid 115 is not energized. In one embodiment, a second elastic member 155 exerts an opposing force from the opposite side of armature 125 to force the armature against the armature retainer 140 and/or to decelerate a movement of the armature with respect to the valve needle 135 in direction away from the magnetic core 120.

(13) The injector 100 may be configured for a fuel flow that starts in an upper part of FIG. 1 and extends along the longitudinal axis 110 into the core 120, through the first elastic member 150, into the valve needle 135 and to the valve assembly 130. From there, the fuel may be injected into a combustion engine when a current flows through the solenoid 115, so that the armature 125 is moved up axially against the core 120, thereby opening the valve assembly 130 through a valve needle 135.

(14) A rectangle with broken line shows an area of FIG. 1 that is presented magnified in FIG. 2.

(15) In an upper area of FIG. 2 it can be seen that the armature retainer 140 fits snugly in the cavity 145 of core 120. In this way, the armature retainer 140 cooperates with the magnetic core 120 to guide the valve needle 135 axially. The tube of the valve needle 135which extends through a central opening in the armature 125may in turn cooperate mechanically with the armature 125 for axially guiding the armature 125.

(16) It is preferred that friction between the member 140 and the core 120 is low. Materials, especially of member 140, may be chosen accordingly. It is furthermore preferred that a radially outer surface of member 140 is spaced from the cavity 145 so that a certain degree of tilting between the valve needle 135and consequently the armature 125and the core 120 may take place.

(17) A sleeve 205 is mounted radially between the tubular body 105 and the armature 125. Preferably, the sleeve 205 extends at least partly into the area of the solenoid 115. In other words, the sleeve 205 or a portion of the sleeve 205 may be circumferentially enclosed by the solenoid 115. The sleeve 205 comprises or consists of a diamagnetic material, the diamagnetic material being for example selected from the group consisting of bismuth, pyrolytic graphites, perovskite copper-oxides, alkali-metal tungstenates, vandanates, molybdates, titanate niobates, NaWO.sub.3, YBa.sub.2Cu.sub.3O.sub.7, TiBa.sub.2Cu.sub.3O.sub.3, Al.sub.xGa.sub.1As and Cr, Fe selenides. The sleeve 205 may also comprise a polymer having a diamagnetic material as one of those mentioned above suspended therein.

(18) The diamagnetic sleeve 205 per definition has a magnetic susceptibility that is negative. In reaction to an external magnetic field, the diamagnetic material of sleeve 205 generates another magnetic field of opposite direction. As the sleeve 205 is disposed laterally to the armature 125, i.e. it extends circumferentially around the armature 125, it may help to reduce or cancel out a radial portion of the magnetic field generated by the solenoid 115 in the region of the armature 125.

(19) When the solenoid 115 is energized, its magnetic field generates an axial force 210 which pulls the armature 125 along longitudinal axis 110 towards the magnetic core 120 which sometimes is also denoted as a pole piece. However, a portion of the magnetic field may induce a first radial force 215. The radial force may act in a radial direction which may not be predictable at the time of assembling the injector and may vary from injection event to injection event, and therefore may be hard to balance. Thus, wear and/or friction may be caused in conventional injectors by this radial force.

(20) However, in case of the injector 100 according to the present embodiment, the same radial component of the magnetic field passes through the sleeve 205 in which an opposing magnetic field is created, exerting a second radial force 220 onto the armature 125 in opposite radial direction. Ideally, the radial forces 215 and 220 cancel themselves out.

(21) FIG. 3 shows a schematic diagram 300 of energy levels of the armatures 125 of different fuel injectors. In a horizontal direction, a displacement of armature 125 in a radial direction x is displayed. In a vertical direction, energy E of the armature 125 is shown. The higher the energy of armature 125 is, the stronger a residual force onto armature 125 in a radial direction may be.

(22) A first point C symbolizes the conditions in a standard injector in which no further means are taken for radial stabilization of the armature 125. It can be seen that the armature 125 is in an unstable equilibrium state. A small displacement may lead to effective forces that increase the displacement.

(23) A second point A shows circumstances on a conventional injector 100 with radial air gap. For small radial displacements of armature 125 the energy level remains constant. However, if the armature 125 is moved in a positive x-direction far enough, the movement is increased. Point A represents an indifferent equilibrium state.

(24) In contrast, point B represents a stable equilibrium state. This represents the configuration of the injector 100 discussed above with respect to FIGS. 1 and 2. Through the use of diamagnetic sleeve 205, both a positive and a negative displacement of armature 125 in a radial direction will lead to an increasing counterforce that moves it back onto longitudinal axis 110. Thus, the radial position of armature 125 is kept stable.