EP3747031A1

EP3747031A1 - Shaped magnetic core for an electromagnetic actuator, and method for producing same

Info

Publication number: EP3747031A1
Application number: EP19700374.2A
Authority: EP
Inventors: Johannes KNUST; Olaf Josef; Guido Bayard
Original assignee: Federal Mogul Valvetrain GmbH
Current assignee: Federal Mogul Valvetrain GmbH
Priority date: 2018-04-20
Filing date: 2019-01-10
Publication date: 2020-12-09
Anticipated expiration: 2039-01-10
Also published as: PL3747031T3; WO2019201479A1; DE102018109516A1; US20210241954A1; EP3747031B1; DE102018109516B4

Abstract

Method for producing a magnetic core for an electromagnetic actuator of an electromagnetic valve drive, wherein the method comprises punching a core blank from a soft-magnetic sheet metal and shaping the core blank. The core blank comprises a base segment with an opening, and several wall segments extending outwards from an outer edge of the base segment. In the shaping process, the several wall segments are bent in a direction substantially perpendicular to the base segment.

Description

REFORMED MAGNETIC CORE FOR AN ELECTROMAGNETIC

ACTUATOR AND METHOD OF MANUFACTURING

Field of the invention

The present invention relates to a deformed magnetic core and a method for producing a deformed magnetic core for electromagnets, in particular for an electromagnetic actuator of e 1 ektromagnetischen valve drive.

State of the art

For camshaft-less valve trains (or valve drives) electromagnetic actuators are used, which are based on the principle of a spring-mass oscillator. Usually, the linear structure actuators used for this purpose essentially consist of a magnet armature which is moved between two electromagnets and two cylindrical pressure springs connected to the armature (more precisely to a shaft of the armature) or the valve. If one of the electromagnets is energized, the system is deflected to the corresponding pole face and the associated valve is brought into the closed or open position.

Depending on the position here is always a compression spring fully loaded while the other spring is only partially stretched. Thus, in the end positions, the kinetic energy of the armature is stored as potential energy in the tensioned springs. After switching off the power, the system oscillates to the other side. By switching off the current in the magnetic core (iron core) of the electromagnet eddy currents, which cause the magnet armature sticks a short time on the magnetic core. This gluing time is undesirable because it limits the maximum speed and makes the control more difficult.

Segmented magnetic cores are used to reduce the eddy currents. For this purpose, very fine slots are introduced into the magnetic cores, which lead to the Eddy currents are reduced. The power consumption and the sticking time of the electromagnetic actuators are thereby reduced. The slots must be very fine, since as little as possible surface or volume of the magnetic core should be lost in order to maintain the performance of the magnet.

Currently, the magnetic cores are made of solid material by machining. The machining is very complicated and leads to a high unit price of the magnetic cores. In particular, the final process step of eroding the slots is time consuming and costly. Another disadvantage of machining is the poor material efficiency. Due to the high material price of the alloys used, e.g. Cobalt-iron alloys with a cobalt content of up to 50%, a machining is particularly uneconomical.

Thus, there is a need for a less expensive manufacturing method which overcomes the aforementioned problems, i. which is less time consuming and costly and which has a lower material consumption.

Summary of the invention

The object is achieved by a method for producing a magnetic core for an electromagnetic actuator of an electromagnetic valve drive comprising punching a core blank from a soft magnetic sheet, the core blank comprising: a bottom segment having an opening and a plurality of wall segments extending from an outer edge of the bottom segment to the outside extend; and forming the core blank, wherein the plurality of wall segments are bent in a direction substantially perpendicular to the ground segment.

According to one aspect of the present invention, the method may further comprise attaching a tubular soft magnetic inner core to the ground segment.

In a further aspect, the method may further include attaching a cylindrical soft magnetic inner core on the ground segment and introducing a perpendicular to the ground segment extending through hole by the Innenkem include.

According to a further aspect, the attachment of the inner core can take place by means of friction welding, laser beam welding or electron beam welding.

In another aspect, the method may further include embossing the soft magnetic sheet prior to the step of stamping or embossing the core blank after the stamping step.

According to a further aspect, the core blank may comprise at least 4 wall segments, preferably 8 to 16 wall segments.

According to another aspect, the wall segments may have substantially the shape of a rectangle.

According to another aspect, the sum of widths of the wall segments after the forming may be smaller than an outer circumference of the magnetic core.

According to another aspect, the distance between each two wall segments after forming in the range between 0.05 mm and 0.3 mm, preferably between 0.1 mm and 0.2 mm.

According to a further aspect, the wall segments may extend in the outward direction equidistant from the floor segment.

In another aspect, the method may further comprise heat treating the magnetic core after reshaping the core blank.

According to a further aspect, the floor segment may have the shape of a circular disk. In another aspect, the stamping may further include stamping a solenoid power supply line opening.

Further, according to the present invention, there is provided a magnetic core for an electromagnetic actuator for an electromagnetic valve train made by any one of the above methods, wherein the magnetic core comprises an outer wall with slits.

According to another aspect, a width of the slots of the magnetic core may range between 0.05 mm and 0.3 mm, preferably between 0.1 mm and 0.2 mm.

Furthermore, according to the invention, an electromagnetic actuator for an electromagnetic valve drive is provided, which comprises a magnetic core produced according to the invention.

Short description of the drawing

In the following, exemplary embodiments of the invention are described in more detail with reference to the figures, wherein

Fig. 1 shows a plan view of a core blank after punching and before forming;

Fig. 2A is a sectional view of the core blank after punching and before forming;

Fig. 2B is a sectional view after forming the core blank;

Fig. 2C is a sectional view after attaching the inner core;

Fig. 3A is a perspective view after forming the core blank;

Fig. 3B shows a perspective view after attaching the inner core; and

4 shows a view of an electromagnetic valve drive.

Hereinafter, the same reference numerals are used for the same or similar elements or components both in the description and in the drawing. It is also a reference list given, which is valid for all figures. The in the figures The embodiments shown are merely schematic and do not necessarily represent the actual size ratios.

Detailed description of the invention

According to the invention, a core blank made of a soft magnetic sheet, i. a sheet metal from a white chmagneti see material, punched. Such a core blank 2 is shown in Fig. 1 in a plan view. The stamped core blank 2 comprises a bottom segment 4 having an opening 8 and a plurality (at least two) of wall segments 6 (only one is provided with a reference numeral in the figure) extending outwardly from an outer edge of the bottom segment 4 - i.e. away from the ground segment. The punched opening 8 forms a passage opening through the floor segment; an edge of the opening is corresponding to an inner edge of the floor segment. Preferably, the opening 8 is arranged centrally in the bottom segment 4. Furthermore, the core blank 1 may optionally include a likewise punched opening for a later power line feed for a magnetic coil used in the finished electromagnetic actuator; i.e. a solenoid power supply line opening 12.

By way of example, the bottom segment 4 in FIG. 1 has approximately the shape of a circular disk. By way of derogation, other forms are possible, e.g. an oval shape, triangular, quadrangular, pentagonal, or more generally n-shaped. The same applies to the shape of the opening, whose shape may also differ from the shape of the bottom segment. The shape is determined in particular by the desired shape of the magnetic core.

Likewise by way of example, the floor segment 4 in FIG. 1 comprises eight wall segments 6, which are regularly arranged around the outer edge or circumference of the bottom segment, so that an angle a of 45 exists between two adjacent wall segments 6. Overall, the core blank in the example of the figure is thus star-shaped. In general, the core blank preferably comprises at least 4, more preferably 4 to 20, most preferably 8 to 16, wall segments. Also, a not regular arrangement is the Wall segments 6 along the outer edge of the bottom segment 4 conceivable.

The wall segments 8 in the figure (which shows a preferred embodiment) have a substantially rectangular shape (ie, the shape of a rectangle) with a width measured along the outer edge of the bottom segment 4 and a length measured perpendicular to it. " Rectangular shape "means here that the width remains the same with increasing distance from the ground segment, ie parallel side edges in the longitudinal direction, but the shape of the other two side edges of the rectangle may differ slightly from the exact rectangular shape, for example adapted to the shape of the outer edge of the bottom segment. Preferably (as shown), the wall segments all have the same width; However, there are also different widths possible. Also, the lengths of the wall segments are preferably the same, i. in the outward direction, the wall segments extend equidistant from the ground segment; whereby also here different lengths are conceivable. It is also possible to deviate from the preferred rectangular shape of the wall segments; e.g. is a parallelogram shape or a stepped shape (several rectangles offset strung together) possible. Here, in particular, the later course of the magnetic field lines is to be considered.

The sum of the widths of the wall segments 6 is preferably substantially equal to the length of the outer edge of the bottom segment 4, i. the circumference of the bottom segment. As a result, after the forming step described below, in which the wall segments 6 are bent over in a direction substantially perpendicular to the bottom segment 4, narrow gaps remain between the wall segments, which prevent eddy currents. "Essentially" means here that the sum of the widths of the wall segments is equal to or slightly smaller than the circumference of the bottom segment. For example, is the difference of the circumference of the bottom segment minus the sum of the widths of the wall segments N times d, where N is the number of wall segments and d is a predetermined minimum distance in the range of 0 mm to 0.3 mm, more preferably 0.1 mm to 0, 2 mm, is. Here, in particular, the design of the forming step is relevant.

The sheet used consists of a soft magnetic material, ie a Ferromagnetic material with low (less than about 1000 A / m) coercive field strength, which can be magnetized relatively easily. Preferably, a cobalt-iron alloy is used. Other possible materials include soft iron or a nickel-iron alloy.

In order to facilitate the subsequent forming small holes can still be provided in the corners, meet at the two wall segments. As will be described below, these holes may also serve to continue the slots formed in the ground segment between the wall segments (after forming).

FIGS. 2A, 2B and 2C show sectional views of the core blank 2 or magnetic core 1 during further method steps.

Fig. 2A shows the core blank 2, which comprises the bottom segment 4 with the opening 8 and the wall segments 6, after punching in a sectional view (eg, a section along the horizontal dotted line in Fig. 1). In addition, it can be seen here that the floor segment 2 has, by way of example, a greater thickness than the wall segments 6. This is achieved by an additional optional embossing step. By embossing is meant here a forming process which enables a thickness structuring of a flat metal component, such as pressing, extruding, possibly accompanied by a change in the dimensions of the metal component in directions perpendicular to the thickness. In particular, the method may include embossing the soft magnetic sheet prior to punching or embossing the core blank after punching. In the latter case, for example, the blank may first be punched from a thicker sheet, and then the wall segments may be lengthened and reduced in thickness by the embossing step to obtain the final core blank. More generally, by embossing the core blank, a thickness structuring can be embossed in order, for example, to achieve greater thicknesses in regions with a higher magnetic field strength. As the "thickness" (of the core blank), the dimension is defined perpendicular to the plane formed by the ground segment that coincides with the plane formed by the original sheet. After the step of punching out and optionally embossing, according to the invention, a forming step takes place in which the plurality of wall segments 6 are bent in a direction substantially perpendicular to the plane formed or defined by the bottom segment 4. Fig. 2B shows the magnetic core 1 after this forming. "Substantially perpendicular" is to be understood here as meaning that small deviations from the 90 ° angle can occur, ie the angle should be between 80 and 100 °, preferably between 85 and 95 °. More generally, larger angles, such as between 70 ° and 1 10 °, conceivable. This is particularly dependent on the ultimately desired shape of the magnetic core.

The forming takes place in a forming machine by means of a suitable tool, so that an outer wall (formed by the bent wall segments) of the magnetic core is generated. For example, The core blank can be pressed by a stamp in a corresponding counter-mold (a cup-shaped negative form), wherein the dimensions (eg the diameter) of the punch correspond approximately to the dimensions of the bottom segment or are slightly smaller and the larger dimensions of the counter-mold the desired Corresponding dimensions of the magnetic core to be produced, so that when pushing the punch in the counter-shape, the wall segments are bent.

By bending the introduced in the art by erosion slots are already included in the outer wall of the magnetic core. The sum of the widths of the wall segments 6 after forming should be smaller than an outer circumference of the magnetic core so that slots are obtained in each case. Furthermore, the distance (measured in the circumferential direction, ie in the direction of the outer edge of the bottom segment) between each two wall segments after the forming is preferably in the range between 0.05 mm and 0.3 mm, more preferably between 0.1 mm and 0.2 mm , This distance corresponds to a width of the slots. Thus, narrow slits are obtained, on the one hand affect the magnetic properties or performance of the magnetic core only slightly and on the other hand prevent eddy currents in the circumferential direction. Erosion of slots can therefore be dispensed with, which leads to a saving of time and costs in production and enables a reduction of the cycle times. At the same time less material needed because the core is not made of solid material machined.

Further, an inner core 10 (a type of dome) may be attached to the ground segment 4. Fig. 2C shows the magnetic core 1 after this optional attachment of the inner core 10. The inner core 10 extends in the same direction in which the wall segments 6 are bent; the corresponding side of the bottom segment 4 is also referred to as the top of the bottom segment. The Innenkem 10 is made of a soft magnetic material, wherein also here preferably a cobalt-iron alloy, a nickel-iron alloy or soft iron is used. The windings of a magnetic coil to be attached (see Fig. 4) extend around the inner core 10 and within the outer wall formed by the bent wall segments 6.

The inner core 10 has a through hole which is aligned with the opening of the bottom segment 4; Here, an anchor shaft (or possibly a valve stem) is passed through during subsequent use in a valve train (see Fig. 4). The Innenkem may already have a tubular shape prior to attachment to the ground segment 4, ie the through hole is present from the outset. By "tubular" is meant a general tubular body, not necessarily a circular tube, but the latter is preferred. Alternatively, first a cylindrical inner core can be attached to the floor segment 4, and then the through hole can be introduced through the inner core in the direction perpendicular to the floor segment. By "cylinder" is here to be understood a general cylinder, ie a body which arises by parallel displacement of a not necessarily circular base along a direction perpendicular to the base. The cylindrical Innenkem is attached to this base on the ground segment, so that the opening of the bottom segment is covered. Subsequently, the through hole is introduced, for example by drilling, so that it passes through the opening. Preferably, a Innenkem which has a circular shape in a plan view or a circular cylinder (the base is thus a circle). More generally, the base may be an oval, triangle, rectangle, n-corner, etc. The same applies to the through hole through the Innenkem, which is preferably circular, however, corresponding to the shape of a typical armature shaft (possibly valve stem). The attachment of the inner core 10 to the ground segment 4 takes place, for example, by friction welding, laser beam welding or electron beam welding. The combination of this joining process with the previous forming process leads to a significantly improved material efficiency compared to a machining. The slots required to minimize power consumption are already contained in the reshaped core by the blank mold.

An edge of the opening of the bottom segment 4 may be adapted to the shape and dimensions of an outer edge of the inner core so that the inner core can be inserted flush with the opening and secured there (e.g., by one of the above welding methods) as shown in Fig. 2C. Alternatively (not shown), the inner core may be larger than the opening in the ground segment and secured to a surface at the top of the bottom segment, friction welding being preferred. In the latter case, dimensions parallel to the ground segment (e.g., a diameter) of the through hole of the inner core correspond to corresponding dimensions of the opening of the bottom segment so that the opening of the bottom segment and the through hole of the inner core smoothly merge. Furthermore, it is possible that the edge of the opening of the bottom segment and the inner core have mutually complementary circumferential steps, which are placed into one another during attachment.

It should also be noted that it is also possible to dispense with the inner core 10. The armature shaft (possibly valve stem) is then guided only through the opening 8 of the bottom segment 4. However, the embodiment with Innenkem is preferred, since this leads to an improvement of the magnetic properties of an electromagnet produced with the magnetic core.

Further, the method may include one or more heat treatments (eg, tempering) of the magnetic core, for example, tempering at a suitable temperature. This can be counteracted by a structural change due to the forming and tensions are reduced. Furthermore, a tempering for adjusting the magnetic Properties of the material used may be helpful. The heat treatment thus takes place after the forming step and, if an inner core is attached, after the inner core has been attached.

FIGS. 3A and 3B show perspective views of the magnetic core 1 after forming the core blank or inner core (FIG. 3A) and after attaching the inner core 10 (FIG. 3B). In both figures, the slots 22 shown as lines between the wall segments 6 can be seen. The magnetic core 1 thus has an outer wall with slots 22, which is formed by the bent wall segments 6. Likewise, a lateral edge of the bottom segment 4 is visible, which has no slots here by way of example. Deviating from this, it is also possible to provide the bottom segment 4 with slots which continue the slots between the wall segments at the bottom. This can e.g. be done by punching out corresponding areas with punching; see. Fig. 1, where correspondingly small holes at the corners, where wall segments meet, are provided. It is also conceivable that the inner core 10, which has no slots in FIG. 3B, is provided with slots on the outside, which are inserted by means of a method known to the person skilled in the art, e.g. Erode. In the space along the inside of the formed by the bent wall segments outer wall, a magnetic coil can be introduced, which extends around the opening and which runs in the case of an attached inner core between Innenkem and wall.

4 illustrates a portion of a valve train employing an electromagnetic actuator having two electromagnets each employing a magnetic core. The electromagnets of the electromagnetic actuator each include the magnetic core 1 and a magnetic coil 14 disposed in the annular space the respective magnetic core is arranged. Through the openings of the magnetic cores 1, an armature shaft 18 of a ferromagnetic (magnetic) armature 16 is guided. An only partially illustrated valve is disposed (in the figure) below the armature shaft 18, wherein a valve stem 24 of the valve is in extension of the armature shaft 18. The valve head, not shown, would be located below the figure. The armature shaft 18 is connected to the armature 16, so attached to this or manufactured in one piece with this. The system is supported by two (pressure) Fedem 20 vibrationally, with a compression spring acts on the upper end of the armature shaft 18 and the other on the valve stem 24. (In principle, it is also possible that the valve stem simultaneously forms the armature shaft, in this case, the valve stem extends through the actuator, the armature 16 is connected to the valve stem and both pressure springs act on the valve stem.) If one of the electromagnets of the electromagnetic actuator is turned on, ie current flows through the respective magnetic coil 14, the armature 16 and the associated armature shaft 18 attracted by this and thus actuated the valve.

Finally, it should be noted that the figures represent a particularly preferred embodiment, which has a rotational symmetry. That the floor segment and the opening in the floor segment are circular and the wall segments all have the same shape and are regularly arranged around the floor segment. Likewise, the inner core has the shape of a hollow circular cylinder. The wall segments accordingly form after forming an annular outer wall which is connected by the bottom segment in the form of a circular disk with the Innenkem. However, it will be understood by those skilled in the art that the method may be practiced with other forms and configurations and that the manufactured magnetic core may be adapted to a predetermined requirement, such as a predetermined outer shape. It is possible to combine the shapes described above in this application for ground segment, opening in the ground segment, wall segments and possibly Innenkem. For example, the ground segment may be rectangular with a round opening; After forming, a cuboid open on one side is then obtained. A corresponding inner core may also have an outer parallelepiped shape with a round through hole.

LIST OF REFERENCE NUMBERS

1 magnetic core

2 core blank

4 ground segment

6 wall segment Opening in the ground segment

internal core

Solenoid power supply line opening

solenoid

anchor

anchor shank

feather

slot

valve stem

Claims

claims

A method of manufacturing a magnetic core (1) for an electromagnetic actuator for an electromagnetic valve train, comprising

Punching a core blank (2) from a soft magnetic sheet, wherein the core blank (2) comprises:

a floor segment (4) with an opening (8) and

a plurality of wall segments (6) extending outwardly from an outer edge of the bottom segment (4); and

Forming the core blank (2), wherein the plurality of wall segments (6) are bent in a direction substantially perpendicular to the bottom segment (4).

The method of claim 1, further comprising

Attaching a tubular soft magnetic inner core (10) on the

Ground segment (4).

The method of claim 1, further comprising

Attaching a cylindrical soft magnetic inner core (10) on the

Ground segment (4); and

Introducing a perpendicular to the ground segment (4) extending

Through hole through the Innenkem (10).

4. The method according to any one of claims 2 or 3, wherein attaching the

Innenkems (10) by means of friction welding, laser welding or

Electron beam welding takes place.

5. The method according to any one of the preceding claims, further comprising

Embossing the soft magnetic sheet prior to the step of punching or embossing the core blank (2) after the stamping step.

6. The method according to any one of the preceding claims, wherein the core blank (2) at least 4 wall segments (6), preferably 8 to 16 wall segments (8).

7. The method according to any one of the preceding claims, wherein the wall segments (6) have substantially the shape of a rectangle.

8. The method according to any one of the preceding claims, wherein the sum of widths of the wall segments (6) after the forming is smaller than an outer circumference of the magnetic core (1).

9. The method according to any one of the preceding claims, wherein the distance between each two wall segments (6) after forming in the range between 0.05 mm and 0.3 mm, preferably between 0, 1 mm and 0.2 mm.

10. The method according to any one of the preceding claims, wherein the wall segments (6) extend in the outward direction equidistant from the ground segment (4).

1 1. A method according to any one of the preceding claims, further comprising

a heat treatment of the magnetic core (1) after the forming of the core blank

(2).

12. The method according to any one of the preceding claims, wherein the bottom segment (4) has the shape of a circular disk.

13. The method of claim 1, wherein the stamping further comprises stamping a solenoid power supply line opening.

14. Magnetic core (1) for an electromagnetic actuator for a

An electromagnetic valve train comprising an outer wall with slots (22), wherein the magnetic core (1) is made by a method according to any one of claims 1-13.

15. Magnetic core (1) according to claim 14, wherein a width of the slots (22) is in the range between 0.05 mm and 0.3 mm, preferably between 0.1 mm and 0.2 mm.

16. An electromagnetic actuator for an electromagnetic valve train comprising a magnetic core (1) according to any one of claims 14 or 15.