WO2001041164A1

WO2001041164A1 - Method for producing an eddy-current-free armature for an electromagnetic actuator

Info

Publication number: WO2001041164A1
Application number: PCT/EP2000/011869
Authority: WO
Inventors: Günter Rudolf FEYERL; Michael Schebitz
Original assignee: Fev Motorentechnik Gmbh
Priority date: 1999-12-04
Filing date: 2000-11-28
Publication date: 2001-06-07
Also published as: DE19958574A1; JP2003515944A

Abstract

The invention relates to a method for producing an armature (1) for use as an adjustment element in an electromagnetic actuator, said armature comprising an armature plate (3) that is linked with a guide pin (2). According to the invention, as the blank acting as the armature plate (3), a green compact that consists of a sinterable ferromagnetic material powder is pressed against the guide pin (2) that consists of a heat-treatable steel. The blank is then heated to sintering temperature and is cooled off.

Description

Name: Process for the production of an eddy current armature for an electromagnetic actuator

description

For a number of applications, an electromagnetic actuator is formed by at least one electromagnet which can be energized, the pole surface of which is assigned an armature at a distance, which is held in a first switching position via a return spring and when the electromagnet is energized against the force of the return spring on the pole surface of the electromagnet is brought into contact. When the electromagnet is de-energized, the armature is moved back into the first switching position by the restoring force of the restoring spring. The actuating element to be actuated is connected to the armature, so that the armature simultaneously forms part of the actuating element.

In addition, electromagnetic actuators are known which have two electromagnets with their pole faces facing one another and arranged at a distance from one another, between which the armature connected to the actuating element is moved back and forth against the force of return springs when the electromagnets are suitably energized. such

Actuators are used, for example, to actuate gas exchange valves on piston internal combustion engines. Here, the gas exchange valve is held in the first switching position by the one of the two electromagnets in the closed position and after switching off the holding current and switching on the catching current for the other electromagnet, the gas exchange valve is held in the open position via the armature. This means that a gas exchange valve, for example in a four-stroke piston internal combustion engine, is actuated with a very high switching frequency depending on the crankshaft speed. Since, despite the high switching frequencies, the very short switching times must be adhered to very precisely, it is the importance that the armature is designed with low eddy currents so that it can detach itself very quickly from the pole face, for example when the holding current is switched off.

Since the anchor plate must have soft magnetic properties on the one hand, and on the other hand the anchor plate is connected to a guide pin which must be low in wear and accordingly should preferably be made from a hardenable steel material, it is not possible to anchor the anchor, i.e. Manufacture anchor plate and guide pin from only one material if optimal results are required. Accordingly, it has already been proposed to connect an anchor plate composed of a plurality of metal sheets to a steel guide pin, in order to take advantage of the low eddy current formation known from sheet metal yoke bodies of transformers or from electromagnets in the case of yoke bodies laminated in this way. One problem here is the high mechanical stress on the armature plate, which arises each time it hits the pole face of an electromagnet.

The invention has for its object to provide a low eddy current armature that meets both the mechanical and the electrical requirements.

To produce an armature for use as an actuating element in an electromagnetic actuator, which has an armature plate connected to a guide pin, a method is provided according to the invention in which a green body made of a sinterable powder is used as the raw part on the guide pin made of a hardenable steel material as the anchor plate is pressed, then the blank is heated, sintered and then cooled. A sinterable powder is expediently used, in which the particles made of ferromagnetic material are largely electrically insulated from one another despite the sintering. This can be achieved by adding sinterable, electrically non-conductive powder share, but preferably caused by powder in which the ferromagnetic and / or electrically conductive powder particles are provided with a sinterable "covering" made of electrically non-conductive materials. In this way, the formation of eddy currents in the finished sintered armature plate is reduced in comparison to a soft magnetic solid metal. With this method it is possible, on the one hand, to produce a solid armature plate, which, on the other hand, due to an appropriate composition of the sinterable sintered powder, has only a slight tendency to form eddy currents when remagnetizing.

In one embodiment, the manufacturing process offers a further advantage if the raw part with the fully sintered anchor plate is rapidly cooled from the sintering temperature to the room temperature range and then heated at least once to the tempering temperature of the steel material, kept at this temperature for a predefinable time and then cooled completely. This procedure takes advantage of the fact that the sintering temperature for the sintering powders in question is considerably higher than the hardness and tempering temperature for a hardenable material, so that after the sintering process has been completed, the further heat treatment can be carried out practically in one heat. Without affecting the structure of the sintered anchor plate, the temperature control during the heating can be carried out in such a way that the structural changes in the heat-treatable steel material are also taken into account. Depending on the type of heat-treatable steel material, it may be expedient to heat it gradually and to keep the temperature at a predetermined temperature during an intermediate temperature step so that the microstructure in the steel material runs smoothly here. Depending on the steel material, such a holding time can take several minutes. There is no impairment of the structure of the sintered anchor plate. In an expedient embodiment of the method, it is provided that at least one radially aligned connecting attachment connected to the guide pin is pressed with the sinterable sintered powder to connect the anchor plate to the guide pin. This results in a positive connection between the guide pin and anchor plate. Depending on the design of the actuator, the anchor plate can be set up perpendicular to the axis of the guide pin, as is required, for example, for the actuators described at the outset for actuating a gas exchange valve. The connecting approach can also be wing-like radial, ie aligned parallel to the axis of the guide pin, as is required, for example, for an actuator for generating a rotary or pivoting movement, in which the anchor plate does not move back and forth in the longitudinal direction of the axis of the guide pin but is pivoted back and forth rotating about the axis of the guide pin.

In a further inventive embodiment of the method, it is provided that the preferably thin, web-shaped connecting projection which extends radially into the anchor plate is provided with openings through which the sintered powder is pressed. This ensures that the web-shaped connection approach not only on its outside from

Sintered powder is enclosed, but also through the perforations, intermediate areas of the connection attachment are penetrated by the sintered powder and, accordingly, also by the finished sintered material. The openings can be, for example, in the form of closed or laterally open

Holes or punched holes are formed. Since the connection approach affects the magnetic and electrical properties of the anchor plate when the material is connected to the guide pin made of tempered steel, it should only have as much "mass" as is absolutely necessary for reasons of strength. The recesses enlarge the "current paths" for corresponding vortex currents and contribute to the reduction of eddy current influences.

In a further advantageous embodiment of the method according to the invention, it is provided that the connecting attachment has a sleeve-shaped middle part made of solid metal, which is connected to the guide bolt, preferably by brazing, after the anchor plate has been sintered on. This makes it possible to select a soft magnetic material or a non-magnetizable and / or electrically poorly conductive material with corresponding strength and conductivity properties for the connection approach with its sleeve-shaped central part, so that only the "bare" guide pin made of a heat-treatable steel material and so that it consists of a "hard magnetic" material. This prevents the formation of eddy currents from being favored via the connection attachment in the anchor plate, which would be the case with a material connection with the guide pin. The desired reduction in eddy current formation is thus observed.

A low-eddy current armature as an actuating element for an electromagnetic actuator with a guide pin made of a tempered steel material, which is connected to an anchor plate sintered from a powder containing ferromagnetic materials, especially if it is produced by the method according to claims 1 to 7 also represents an invention.

In an embodiment of the anchor according to the invention, it is provided that the guide bolt is provided with at least one radially oriented, essentially flat connecting projection, which is enclosed by the material of the anchor plate.

In a preferred embodiment of the invention, it is further provided that the flat connection approach with recesses is provided, which are penetrated by the material of the anchor plate.

In one embodiment of the invention, the connection attachment can be integrally connected to the guide pin, while in another embodiment the connection attachment has a connection sleeve which encloses a partial area of the guide pin and is preferably connected to it by hard soldering.

The invention is explained in more detail with reference to schematic drawings of exemplary embodiments. Show it:

1 is an axial section of an armature for an actuator for generating a back and forth movement,

2 is an axial section of an armature for an actuator for generating a pivoting movement,

Fig. 3 shows a section. the line III-III in Fig. 1,

Fig. 4 shows a modified embodiment of an anchor. Fig. 1.

The sectional view in Fig. 1 shows an anchor 1, which consists essentially of a guide pin 2 and an anchor plate 3 firmly connected thereto. The armature is used in an actuator in which a corresponding arrangement of the electromagnets results in a back and forth movement in the direction of the longitudinal axis 5 of the guide bolt 2 (arrows 4).

As can be seen from the sectional view, the guide pin 2 has a web-shaped extension 6 at one end, for example in the form of a circular collar, which is enclosed by the material of the anchor plate 3. The web-shaped extension 6 is shown only schematically with a large number of provided openings 7, which can be arranged for example in the manner shown in Fig. 3. The web-shaped extension 6 can also be formed by radially oriented arms or fingers, so that the material of the anchor plate completely surrounds it. The spaces between the arms represent openings in the sense of the invention. The shape, size and contour of the openings 7 or the parts of the web material delimiting them can be designed as desired if only the conditions for strength and eddy current behavior are observed.

To manufacture such an anchor, a blank is first produced. Here, the anchor plate 3 is pressed as a so-called green body from a sinterable powder, which contains ferromagnetic material, from the guide bolts 2, which are made from a hardenable steel material. The pressing process gives the anchor plate its desired dimensions, with some of the powder being pressed through the openings 7 and thus, despite the relatively wide extension of the web-shaped extension 6 into the material of the anchor plate, also in the area directly in the vicinity of the guide pin a continuous connection of the sintered material to both sides of the web-shaped extension 6 is created. All edges and transitions of the web-shaped extension 6, which are enclosed by the material of the anchor plate 3, must be well rounded in order to avoid notch effects which could lead to cracks when the anchor is subjected to mechanical stress.

The raw part thus produced is then heated to sintering temperature and cooled again after the anchor plate has been sintered. The unmachined part can either be completely cooled or, at least once, "heated" to the tempering temperature of the steel material used for the guide pin 2 and kept at this temperature for a predetermined time and then completely cooled. Since the tempering temperature for the

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Claims

Expectations:

1. A method for producing an armature (1) for use as an actuating element in an electromagnetic actuator, which has an anchor plate (3) connected to a guide pin (2), characterized in that the raw part on the guide pin (2 ) as an anchor plate (3), a green compact made of a powder containing sinterable ferromagnetic material is pressed, then the blank is heated to sintering temperature and then cooled.

2. The method according to claim 1, characterized in that the blank with the finished sintered anchor plate (3) cooled rapidly from the sintering temperature to the room temperature range and then heated at least once to the tempering temperature of the steel material, held at this temperature for a predetermined time and then cooled completely.

3. The method according to claim 1 or 2, characterized in that for connecting the anchor plate (3) to the guide pin (2) at least one with the guide pin (2) connected radially aligned web-shaped connecting projection (6) is pressed with the sinterable powder ,

4. The method according to any one of claims 1 to 3, characterized in that the radially up to the anchor plate (3), preferably thin-walled web-shaped connecting projection (6) is provided with openings (7) through which the powder is pressed.

5. The method according to any one of claims 1 to 4, character- ized in that the connecting projection (6) has a sleeve-shaped central part (8), which after sintering the An- kerplatte (3) with the guide pin (2.2) is preferably connected by brazing.

6. The method according to claim 5, characterized in that a low-eddy current soft magnetic material is used for the connecting approach (6) with a sleeve-shaped central part (8).

7. The method according to any one of claims 1 to 6, character- ized in that for the anchor plate at least one pre-pressed green part is made, which is assembled with the connecting approach, and that the missing part is then pressed in powder form or as a corresponding pre-pressed green part ,

8. Low eddy current armature as an actuating element for an electromagnetic actuator, with a guide pin (2) made of a tempered steel material, which is connected to a low eddy current anchor plate (3) sintered from a composition which is soft-magnetic powder, in particular according to the method according to. claims 1 to 7 manufactured anchor.

9. Anchor according to claim 8, characterized in that the guide pin (2) is provided with at least one radially oriented substantially flat connecting projection (6) which is enclosed by the material of the anchor plate (3).

10. Anchor according to claim 8 or 9, characterized in that the guide pin (2) perpendicular to the plane of the anchor plate

(3) is aligned.

11. Anchor according to claim 8 or 9, characterized in that the guide pin (2.1) extends substantially in the central plane of the anchor plate (3.1).

12. Anchor according to one of claims 8 to 11, characterized in that the flat connection projection (6) is provided with openings (7) which are penetrated by the material of the anchor plate (3).

13. Anchor according to one of claims 8 to 12, characterized in that the connecting projection (6) is integrally connected to the guide pin (2).

14. Anchor according to one of claims 8 to 12, characterized in that the connecting projection (6) has a sleeve-shaped central part (8) which surrounds a part of the guide bolt (2.2) and is preferably connected to this by brazing.

15. Anchor according to claim 14, characterized in that the connecting projection (6) with its sleeve-shaped central part (8) also consists of a soft magnetic material.