Electromagnetically actuatable valve

1. Field of the Invention

The present invention relates to an electromagnetically actuatable valve, in particular a fuel injector, having a magnetic actuator, as well as a method for manufacturing components of a magnetic actuator, for example, a magnet armature.

2. Description of the Related Art

High-pressure injectors of the related art are essentially designed as conventional solenoid switching valves having a coil and components of a magnetic actuator, for example, a magnet armature, an internal pole, an external pole, which are manufactured as turned parts from a soft magnetic bar material. The electrical properties of the material and the 360°-closed contour of the components cause eddy current losses and consequently a reduced switching time or dynamics of the fuel injector when the magnetic field is built up and reduced during operation.

The electromagnetically actuatable valve according to the present invention has the advantage over the related art that it has components of a magnetic actuator such as a magnet armature and/or an internal pole and/or an external pole, which make it possible to considerably reduce the eddy current losses in the case of magnetic field changes and significantly reduce the valve's switching time. According to the present invention, this is achieved in that the valve has at least one component of a magnetic actuator having a plurality of sectors made of soft magnetic material and a plurality of insulating separating webs, a separating web being situated between each two neighboring sectors and entirely separating the neighboring sectors from one another electrically. The components of the magnetic actuator thus have at least two soft magnetic sectors and two insulating separating webs.

Preferably, the separating webs are in this case manufactured from a material which includes a ceramic. The electrically non-conductive properties of the ceramic material ensure that the individual adjacent sectors of the components of a magnetic actuator are reliably separated or insulated electrically.

The valve preferably includes at least one component of the magnetic actuator having exactly four sectors and four separating webs. As a result, even a small number of sectors and separating webs causes the eddy current losses to be reduced drastically in the case of magnetic field changes.

According to another preferred embodiment, the separating webs have a width which is selected in such a way that neighboring sectors are reliably separated in a straight manner from one another electrically. By minimizing the width and the material portion of the separating webs, only a slight amount of soft magnetic material of the magnet armature is lost, thus ensuring that the strength of the magnetic circuit is essentially consistent.

Preferably at least one component of a magnetic actuator is manufactured using a PIM method (powder injection molding method). Using this multi-component powder injection molding process instead of a turning process makes it possible to manufacture components of a magnetic actuator with short production times and low unit costs in a simple way. The method according to the present invention may be designed in such a way that the insulating separating webs are manufactured in a first step, the insulating separating webs are then held mechanically in a die, and the sectors made of soft magnetic material are subsequently injection-molded. Alternatively, the soft magnetic sectors may be manufactured in a first step. Subsequently, these sectors are placed into a die and held in position with the aid of a magnetic field, and the separating webs are injection-molded into the intermediate spaces between the soft magnetic sectors in a subsequent step. Thus, a cost-effective manufacture of a component for a magnet armature may be implemented according to the present invention, the component having thin-walled, electrically non-conductive separating webs between soft magnetic sectors. This makes it possible to minimize the formation of eddy currents which counteract the build-up and reduction of fields. The separating webs must be as thin-walled as possible, so that little magnetic material volume is lost, which would negatively influence the achievable magnetic force. The method according to the present invention demonstrates for the first time a production-oriented implementation of the relatively demanding manufacture, since the separating webs or the soft magnetic sectors must be held at a distance in order to be able to manufacture the particular other element with the aid of an injection molding process. According to the present invention, it is thus possible to use a multi-component PIM method for manufacturing one or multiple components of a magnetic actuator such as a magnet armature or a pole core, i.e., internal pole, or a valve jacket, i.e., external pole (feedback element). Particularly preferably, the soft magnetic sectors may be manufactured with the aid of a metal injection molding method (MIM). The insulating separating webs may preferably be manufactured with the aid of a ceramic injection molding method (CIM). The soft magnetic sectors may be positioned in an injection molding die with the aid of a magnetic force, so that open spaces are present between them for the insulating separating webs to be injection-molded. The separating webs may be held in the injection molding die mechanically. Thus, a very economical manufacturing method is achievable.

The method according to the present invention for manufacturing a component of a magnetic actuator having a plurality of sectors made of soft magnetic material and a plurality of insulating separating webs with the aid of a PIM process makes it possible to economically manufacture a component in which the switching times and in particular the break times are drastically reduced, thus resulting in a significantly reduced amount of fuel needed for injection into the combustion chamber when the component is used in a motor vehicle, for example. The reduced injection amount improves the idling behavior of the engine and makes an improved multiple injection of the fuel injectors possible. This results in a significantly improved exhaust gas behavior of the engine.

FIG. 1 shows a schematic sectional view of a magnet armature of a fuel injector.

FIG. 2 shows a perspective representation of a magnet armature of the fuel injector according to the present invention.

With reference to FIGS. 1 and 2 , a fuel injector for injecting fuel according to a preferred exemplary embodiment of the present invention and a method for manufacturing a magnet armature of a magnetic actuator of fuel injector 1 are described in detail below.

As is apparent from the perspective representation of FIG. 1 , the valve includes a magnetic actuator 1 having a magnet armature 3 , a pole core 31 , a valve jacket 32 as a feedback element and a coil 2 which surrounds magnet armature 3 . Magnet armature 3 manufactured from a soft magnetic material has a central through opening 6 situated in an axial direction A, a valve needle (not shown in the representation) being situated in the through opening. Furthermore, magnet armature 3 has four fuel openings 7 running in axial direction A, each of which being situated in one of four sectors 4 . As is further apparent from FIG. 2 , each sector 4 includes essentially one fourth of the volume of magnet armature 3 in the circumferential direction. An insulating separating web 5 made of a ceramic material is situated between each two neighboring sectors 4 , the separating web electrically separating or insulating adjacent sectors 4 . As an alternative to the specific embodiment shown here, the number of sectors 4 or separating webs 5 may be varied appropriately according to a desired function of magnet armature 3 in fuel injector 1 ; however, at least two separating webs must be present.

A component of the magnetic actuator is manufactured using a multi-component powder injection molding process (PIM process). The component, such as a magnet armature, may be manufactured using two alternative methods. Since the component is formed from two component groups, namely sectors 4 and separating webs 5 , a first of the two component groups may be manufactured, preferably with the aid of an injection molding method, in a first step. In a next step, the first component group is then positioned in an injection molding die, and subsequently the second component group is injection-molded in the intermediate spaces among the portions of the first component group using an injection molding method. If the first component group is made up of insulating separating webs 5 , these are held mechanically in the injection-molding die and the soft magnetic sectors 4 are then injection-molded between separating webs 5 using a metal injection-molding method. If the first of the component groups are soft magnetic sectors 4 , sectors 4 are manufactured with the aid of a metal injection molding method and subsequently held in the injection molding die with the aid of a magnetic field. Separating webs 5 are then injection-molded between the intermediate spaces of soft magnetic sectors 4 with the aid of a ceramic injection molding method. Preferably, powder injection molding methods are used as injection molding methods.

The valve according to the present invention and the manufacturing method according to the present invention significantly improve the dynamics characteristics, which are desired and required in particular in high-pressure injectors, according to the thus achievable reduction in eddy current losses, which contributes to considerably improved fuel consumption and emission characteristics of the engine.