CN111354559A

CN111354559A - Fixing device and method for forming aligned magnetic cores

Info

Publication number: CN111354559A
Application number: CN201911336653.6A
Authority: CN
Inventors: 荣传兵; 梁峰; 迈克尔·W·德格纳
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2018-12-21
Filing date: 2019-12-23
Publication date: 2020-06-30
Also published as: DE102019135634A1

Abstract

The present disclosure provides "fixtures and methods for forming aligned magnetic cores. Magnetic cores, methods of forming the same, and fixtures are disclosed. The magnetic core may comprise a magnetic body comprising magnetic particles and a magnetic flux path, the magnetic particles being aligned in a plurality of different directional alignments to conform to the magnetic flux path. The particle orientation of the core may be provided by a fixture comprising an electrical circuit and/or a permanent magnet. The fixture may be configured to generate a magnetic field that approximates, simulates, or corresponds to a magnetic flux path in the magnetic core once the magnetic core is affixed and in use. When the particles of the magnetic core are in an unconsolidated state, the magnetic field may orient the particles such that the particles are aligned in a plurality of directional alignments that approximate, mimic, or correspond to magnetic flux paths in the magnetic core.

Description

Fixing device and method for forming aligned magnetic cores

RELATED APPLICATIONS

This application is a partial continuation of U.S. serial No. 15/962,268 filed on 25/4/2018, U.S. serial No. 15/962,268 is a division of U.S. serial No. 14/535,807 filed on 7/11/2014, the disclosures of which are incorporated herein by reference in their entirety.

Technical Field

The present disclosure relates to aligned magnetic cores and fixtures and methods for manufacturing the aligned magnetic cores.

Background

Electric machines convert energy through electromagnetic interaction, such as converting electricity to electricity (transformers), converting electricity to mechanical power (motors), or converting mechanical power to electricity (generators). One factor affecting energy conversion is the magnetic core material, which is typically formed from a stack of electrical steel (also referred to as silicon steel). In addition to the motor, the magnetic core in the inductor also has an effect on the performance of the inductor. However, core losses (also referred to as iron losses) in the magnetic core can result due to the alternating magnetic field inside the material, especially during high frequency operation. Core loss typically includes three components: hysteresis loss, eddy current loss, and excess loss (or abnormal loss). Hysteresis loss is frequency independent, while eddy current loss and excess loss are both frequency dependent.

Since fuel economy is an important factor in Electric Vehicles (EVs), such as Hybrid Electric Vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and Battery Electric Vehicles (BEVs), reducing core losses and increasing induction (magnetic flux density) in magnetic cores, such as rotor cores and stator cores, of electric machines and power electronics, such as inductor cores, may be a goal. Conventional core formation processes typically reduce losses by sacrificing other magnetic properties, or enhance magnetic properties such as magnetic flux density, but sacrifice loss performance.

One common method of reducing core loss in magnetic cores is to reduce the lamination thickness of electrical steel by mechanical rolling, including hot and cold rolling. Magnetic cores with thinner laminations have significantly lower eddy current losses, and thus lower core losses, than thicker laminations. Another way to reduce core loss is to control the chemical composition, e.g., the content of Si and Al, in the electrical steel. Since Si and Al increase the electrical resistivity of electrical steel, Si and Al are generally controlled during the manufacturing process to reduce eddy current losses. Typically 2-3% Si is used in non-oriented electrical steels and about 6% Si is used in grain oriented electrical steels. Although the core loss is significantly reduced by both methods, it is still problematic, especially for high frequency applications. Another method to reduce core loss is to produce magnetic powders that are sintered directly into bulk cores with or without insulating coatings on the magnetic particles. A similar approach is to mix magnetic powder with a binder and then press it into a near-formed device. However, the use of a binder may reduce the magnetic flux density and permeability of the core.

Disclosure of Invention

In at least one embodiment, there is provided a magnetic core comprising a magnetic body comprising magnetic particles and a magnetic flux path, the magnetic particles being aligned in a plurality of different directional alignments to conform to the magnetic flux path. Each alignment may be a primary alignment with respect to the magnetic body. In one embodiment, the magnetic body has an internal cavity. The plurality of directional alignments may extend around a perimeter of the internal cavity.

In one embodiment, the magnetic core is an inductor core. In another embodiment, the magnetic core is a stator core including a plurality of stator teeth and a plurality of stator slots between the stator teeth. The plurality of directional alignments may include a plurality of arc alignments around the stator slot from one stator tooth to another stator tooth. In another embodiment, the magnetic core is a rotor core including a plurality of permanent magnets disposed therein. The plurality of directional alignments may include a plurality of alignments extending between the permanent magnets and the outer periphery of the rotor core.

In at least one embodiment, a fixture for aligning particles in a magnetic core is provided. The fixture may include one or more internal magnets configured to be located inside the core, the internal magnets configured to generate a magnetic field in the magnetic core and align the particles in multiple directional alignments.

The internal magnet may be configured to generate a magnetic field in the magnetic core that mimics a magnetic flux path of the magnetic core. Each internal magnet may have a north (N) side and a south (S) side. The fixture may include a plurality of internal magnets and a plurality of external magnets configured to be located outside of the core and each internal magnet may form a magnet pair with an external magnet. Each magnet pair may have an N-side facing each other or an S-side facing each other, and adjacent magnet pairs may have opposite N and S-side configurations.

In one embodiment, the magnetic core is a stator core having a plurality of stator teeth and a plurality of stator slots between the stator teeth. The internal magnet may be configured to generate a magnetic field in the stator core and align the particles in a plurality of arc alignments around the stator slot from one stator tooth to another stator tooth. The internal magnet may be arranged to be located at the tip of the stator tooth or in the stator slot. In another embodiment, the magnetic core is a rotor core and the internal magnets are rotor permanent magnets that remain in the rotor core after consolidation.

In at least one embodiment, a fixture for aligning particles in a magnetic core is provided. The fixture may include one or more inner conductors configured to be located inside the core and to carry current in a first direction and one or more outer conductors configured to be located outside the core and to carry current in a second direction opposite the first direction. The inner and outer leads may be configured to generate a magnetic field in the magnetic core.

In one embodiment, the inner and outer conductive wires are configured to generate a magnetic field in the magnetic core and align the particles in a plurality of directional alignments that simulate a magnetic flux path of the magnetic core. The fixation device may include a plurality of inner wires and a plurality of outer wires, and each inner wire may form a wire pair with an outer wire.

Drawings

FIG. 1 is a flow diagram of a method of forming a sintered magnetic core according to one embodiment;

FIG. 2 is a flow diagram of a method of forming a bonded magnetic core according to one embodiment;

FIG. 3 is a schematic diagram of a rectangular inductor core having a magnetic flux direction along its periphery;

FIG. 4 is a schematic diagram of a fixture for applying a magnetic field to a rectangular inductor core using one or more circuits according to one embodiment;

FIG. 5 is a schematic diagram of a fixture for applying a magnetic field to a cylindrical inductor core using one or more circuits according to one embodiment;

FIG. 6 is a schematic diagram of a fixture for applying a magnetic field to a rectangular inductor core using a plurality of permanent magnets according to one embodiment;

FIG. 7 is a finite element analysis simulation of the magnetic field of FIG. 6;

FIG. 8 is a schematic diagram of a fixture for applying a magnetic field to a cylindrical inductor core using a plurality of permanent magnets according to one embodiment;

FIG. 9 is a schematic diagram of a fixture for applying a magnetic field to a rectangular inductor core using a plurality of permanent magnets and cores according to one embodiment;

FIG. 10 is a graph of magnetization versus field strength in an aligned core compared to an isotropic core;

FIG. 11 is a schematic view of a fixture for applying a magnetic field to a stator core using one or more circuits according to one embodiment;

FIG. 12 is a schematic view of another fixture for applying a magnetic field to a stator core using one or more circuits according to one embodiment;

FIG. 13 is a schematic view of a fixture for applying a magnetic field to a stator core using a plurality of permanent magnets according to one embodiment;

FIG. 14 is a schematic view of another fixture for applying a magnetic field to a stator core using a plurality of permanent magnets according to one embodiment; and

FIG. 15 is a schematic view of a fixture for applying a magnetic field to a rotor core using a plurality of permanent magnets according to one embodiment.

Detailed Description

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

As described in the background, conventional core processing typically requires a choice between good magnetic properties and good loss performance (i.e., low loss). The present disclosure provides methods and fixtures for forming magnetic cores having both good magnetic properties and low loss, or that sacrifice one property less than another, relative to conventional magnetic cores. In at least one embodiment, a magnetic core is formed having a particle orientation along a specified predetermined or preferred direction or path. Particle orientation may be provided by applying a specified magnetic field to the magnetic core during processing. The magnetic field may be complex and/or multi-directional (e.g., not a single straight line). The magnetic field direction/path (and corresponding particle alignment) may coincide with, approximate or correspond to the direction of magnetic flux that will occur in the core during use. The degree of particle orientation in magnetic cores produced by this method may be high, but may also be moderate or low, depending on factors such as the magnetic powder, the strength of the magnetic field, the pressing conditions, the binder, etc. The degree of particle orientation may be adjusted based on the required or desired characteristics of the magnetic core.

The magnetic core may be formed using any suitable process, including sintering and bonding magnetic powders. The magnetic powder may comprise any magnetic material that can be sintered or bonded to make a powder core, such as ferrite particles. The magnetic field may be applied during formation of the core using any suitable method, including a fixture having an electrical circuit with one or more current carrying wires and/or arranged permanent magnets. The properties of a magnetic core formed from any suitable magnetic material, including electrical steel, may be improved (e.g., by heat treatment under a magnetic field). The disclosed magnetic core may be suitable for many applications where improved directional permeability and magnetic flux density are beneficial. For example, the disclosed magnetic cores may be used in inductors, transformers, generators, stators, rotors, or any other device having preferred and better characteristics in certain directions.

Referring to fig. 1, in at least one embodiment, the particle-oriented magnetic core may be formed by sintering magnetic powder. The method 10 for forming a sintered core may include preparing a magnetic powder at step 12. Magnetic powders such as ferrite, ferrosilicon or other magnetic powders may be prepared by any suitable process. For example, powders may be prepared by milling, vapor deposition, chemical synthesis, or other techniques. In at least one embodiment, the powder is prepared to have a low number of particles per particle (e.g., a mean or average particle per particle). In one embodiment, the microparticles comprise up to 20 particles, and in other embodiments, up to 10 particles. In another embodiment, the microparticles comprise up to 5 particles. In another embodiment, the microparticles comprise 1 to 3 particles. In another embodiment, the microparticles are single crystals (e.g., single particles). The number of particles per particle may be applied to all or substantially all of the particles in the powder, or the number of particles per particle may be an average. However, it should be understood that machining tolerances may result in some powders having particles with different numbers of particles. The low number of particles per microparticle allows for easier alignment of the microparticles in subsequent alignment steps. A single particle per particle may provide the simplest alignment. The microparticles may have any suitable size or diameter. In one embodiment, the size of the particles is 1nm to 10mm, or any subrange therein. To provide increased core densification, powders having a range of particle sizes may be used. For example, the powder may include submicron particles, particles of 1-10 μm, particles of hundreds of μm, and particles of 1-10 mm.

At step 14, the powder may be mixed with or coated with an insulating material. The high resistance of the insulating material reduces eddy current losses in the magnetic core. In one embodiment, the magnetic powder may be mixed with an insulating material, which may be any suitable dielectric or high resistance material. Non-limiting examples of insulating materials may include silicon dioxide, ferrite, phosphate binders, teflon (PTFE) binders, and the like. Alternatively, the magnetic powder may be coated with an insulating material such that each particle has a core/shell configuration with the magnetic material as the core and the insulating material as the shell. The magnetic powder may be coated using any suitable method, such as chemical solution, vapor deposition, sputter coating, and the like. The magnetic powder may also be oxidized by a controlled oxidation process to form an insulating layer on the particles. The above-described insulation methods may be used alone, or any combination thereof may be used to increase the resistance of the magnetic core.

At step 16, the magnetic powder may be consolidated and aligned. Conventional compaction can result in non-uniform densities in the green compact, which in turn can result in significant shape variations after sintering. In one embodiment, a compaction or agitation process may be applied during consolidation to provide a more uniform compact and reduce or eliminate shape changes after sintering. The compaction process may include pneumatic compaction, mechanical compaction, ultrasonic compaction, or other methods of compacting or agitating the powder. Additionally, any combination of compaction processes may be performed sequentially or simultaneously. Pneumatic tamping may include applying air pressure to the powder and/or the mold by controlling the pressure, air flow load, speed, and time. Mechanical compaction may include compacting the powder and/or the mold using physical contact using manual or automated methods. Ultrasonic compaction may include the use of ultrasonic waves to compact/vibrate the powder and/or the die by controlling the ultrasonic power, frequency, and time.

The alignment process includes applying a magnetic field to the powder while the powder is in the mold (e.g., not consolidated) such that the particles of the powder are aligned along the magnetic field (e.g., along their easy axis). The magnetic field may be applied in the shape or path of the magnetic flux direction in the core, thereby increasing the permeability and flux density in the magnetic flux direction of the finished core. Additional description of the fixture and method for generating a magnetic field is included below in this disclosure. The magnetic field may be applied while the tamping process is being performed. The tamping/agitation generated during tamping may allow the magnetic powder to rotate and more easily orient itself, aligning the easy axis of magnetization of the magnetic powder with the magnetic field. In addition, as mentioned above, alignment in the magnetic field is further facilitated if each particle has a single or only a few particles. To further assist and facilitate the rotation of the magnetic particles during the alignment process, a lubricant may be added to the powder during this step. Non-limiting examples of suitable lubricants can include surfactants, calcium stearate, polyethylene glycol, sorbitol, glyceryl monostearate, or others, and mixtures thereof.

At step 18, an optional pressing process may be performed. Any suitable pressing method may be performed to increase the density of the magnetic core, such as uniaxial pressing. A magnetic field may be applied during the pressing step 18 to maintain or further align the particles in the mold. The magnetic field may be the same as the magnetic field applied in step 16. As a result of the compaction process in step 16, the density of the green compact resulting from compaction may be substantially uniform.

At step 20, the magnetic powder may be sintered to consolidate the powder and form a finished magnetic core. The sintering temperature may be any suitable temperature for consolidating the powder, such as from 600 ℃ to 1,500 ℃. The sintering time may be any suitable time for the powder to consolidate, for example from 10 minutes to tens of hours. Generally, a higher temperature will require a shorter sintering time and vice versa. A magnetic field may be applied during the sintering step 20 to maintain or further align the particles in the mold. The magnetic field may be the same as the magnetic field applied in steps 16 and/or 18. As a result of the compaction process in step 16, the density of the green compact resulting from compaction may be substantially uniform. After sintering, a finished magnetic core is formed having aligned particles with increased permeability and flux density along the path of the aligned particles formed using a predetermined custom magnetic field applied during consolidation 16 and optionally pressing 18 and/or sintering 20 steps.

Further, in some embodiments, the magnetic powder (or solid sample) may be heated while applying an external magnetic field prior to sintering. In one or more embodiments, where a magnetic field is applied during the heating step, the magnetic field may be an external magnetic field. As in the compaction process of step 16, the powder may be compacted while an external magnetic field is applied to further align the magnet powder. In at least one embodiment, a current is applied to the magnetic powder after it is aligned and densified to generate heat (i.e., joule heating). In at least one embodiment, the current is about 5A to 150A, in other embodiments about 10A to 125A, and in still other embodiments about 15A to 100A. In some embodiments, the current heats the container to generate heat in the magnetic powder. The container may be used as a heating medium during the annealing step. The container may be any suitable electrically conductive material, such as, but not limited to, graphite. In certain embodiments, at least the bottom of the container comprises an insulating material, such as, but not limited to, a ceramic. In other embodiments, the bottom and top of the container are conductive, while the sides of the container are insulating material. In another embodiment, the magnet powder may be heated by placing the powder assembly into a coil carrying a high frequency current (i.e., induction heating). In at least one embodiment, the high frequency is about 5kHz to 500kHz, in other embodiments about 10kHz to 450kHz, and in still other embodiments about 15kHz to 400 kHz. In certain embodiments, the current is about 5A to 150A, in other embodiments about 10A to 125A, and in still other embodiments about 15A to 100A. Due to the high frequency current in the coil, the alternating magnetic field generates eddy currents in the magnet powder assembly, which in turn generates heat in the magnet powder assembly. In some embodiments, to keep the magnet powder aligned, a DC current component may be added to the current in the coil.

Similar to a sintering furnace, the generated heat melts the rare earth rich grain interphase for forming the soft magnetic core. An external magnetic field may be applied until the magnet powder temperature reaches the curie temperature of the main phase of the magnet powder to ensure that the magnetic particles are aligned after sintering. The curie temperature may or may not be higher than the melting point of the interface phase of the main phase of the magnet powder. The powder component may be a soft ferrite,Pure iron, iron silicon, or other suitable soft magnetic core material. However, as an example of a material having a curie temperature relative to the melting point, rare earth examples (e.g., neodymium magnets, where Nd is discussed herein)₂Fe₁₄The curie temperature of B is lower than the melting point of the rare earth-rich phase). In some embodiments, the curie temperature is above the melting point of the interphase. For example, in SmCo magnets, the Curie temperature of SmCo is higher than the melting point of the rare earth-rich grain interphase. As such, in the example used for a SmCo magnet, the external magnetic field is maintained at a temperature above the SmCo phase, about 800 ℃. After the magnetic powder reaches the curie temperature of the main phase, the magnetic powder becomes paramagnetic and the natural demagnetization is eliminated. Therefore, the external magnetic field can be removed to reduce power consumption. For example, no external magnetic field need be applied during sintering as in other embodiments.

In some embodiments, after heating with the external magnetic field, the sintering step 20 may be performed at a heating temperature above the melting point of the rare earth-rich phase. The melting point may be, but is not limited to, about 500 ℃ to 900 ℃. The sintering step melts the rare earth rich phase around the grain interface, causing the powders to stick together in a solid compact. As the sintering temperature is further increased, the density of the compact increases and the particles start to grow. The particle size can be optimized by time and temperature selection during sintering to achieve the desired magnetic properties in the final magnet. After sintering, the magnet is cooled and has improved alignment, since the magnetic powder can be heated while being exposed to an external magnetic field.

Referring to fig. 2, in at least one embodiment, a particle-oriented magnetic core may be formed by bonding magnetic powders. The method 30 for forming a bonded core may include preparing a magnetic powder at step 32. The magnetic powder may be prepared in a similar manner as described above with respect to step 12. At step 34, the magnetic powder may be mixed with a lubricant and/or an insulating material. The insulating material and lubricant may be similar to those described above with respect to step 14. Thus, steps 32 and 34 will not be described in detail.

To prepare a bonded core rather than a sintered core, a binder may be used to consolidate and secure the magnetic powder (and any insulating or lubricating materials present). Any suitable binder may be used, such as thermosets, thermoplastics, elastomers, inorganic ceramic binders, high temperature ceramic binders, and the like. Non-limiting examples of thermosets that can be used as the binder are epoxy resins, which can be phenolic epoxy resins (phenoolic) or novalac epoxy resins (novalac). Non-limiting examples of thermoplastics that may be used as the binder are polyamides, such as polyphenylene sulfide (PPS). Non-limiting examples of elastomers that may be used as the adhesive include nitrile rubber, polyethylene rubber, and vinyl rubber.

At step 36, a magnetic field may be used to align the magnetic powder. A mixture of magnetic powder and binder (plus any lubricant or insulating material) may be introduced into the mold while the binder is in a liquid or uncured state (e.g., unconsolidated). A magnetic field may be applied to the mixture and/or the mold while the binder is in a liquid or uncured state to align the magnetic particles in a preferred pattern or direction. Since the binder has not yet cured, the particles are more easily aligned by the magnetic field because they can rotate freely, which can allow the magnetic powder itself to be more easily oriented so that their easy axis of magnetization is aligned/parallel with the magnetic field. As mentioned above, the rotation may be further facilitated by using microparticles with one or several particles. The magnetic field may be applied in the shape or path of the magnetic flux direction in the core, thereby increasing the permeability and flux density in the magnetic flux direction of the finished core. Additional description of the fixture and method for generating a magnetic field is included below in this disclosure. Although not required, a compaction process similar to that described in step 16 may be applied to the mixture of binder and powder during the alignment process.

At step 38, an optional pressing process may be performed. Any suitable pressing method may be performed to increase the density of the magnetic core, such as compaction (e.g., uniaxial pressing), extrusion, or injection molding. In one embodiment, the adhesive used may be a thermoset when compression is performed. In another embodiment, the adhesive may be an elastomer or a thermoplastic when extrusion is performed. In another embodiment, the adhesive may be a thermoplastic when injection molding is performed. A magnetic field may be applied during the pressing step 38 to maintain or further align the particles in the mold. The magnetic field may be the same as the magnetic field applied in step 36.

At step 40, the mixture of magnetic powder and binder may be cured. The curing time and temperature may vary depending on the type of binder used. Some adhesives may not require the application of heat and may be cured at room or ambient temperature. A magnetic field may be applied during the curing step 40 to maintain or further align the particles in the mold. The magnetic field may be the same as the magnetic field applied in steps 36 and/or 38. After curing, a finished magnetic core is formed having aligned particles with increased permeability and flux density along the path of the aligned particles formed using a predetermined custom magnetic field applied during the aligning step 36 and optionally the pressing step 38 and/or the curing step 40.

The magnetic field applied in the sintered or bonded magnetic cores described above may provide a magnetic core suitable for any application where anisotropic or directional magnetic properties (such as permeability, induction/flux density, coercivity, core loss, etc.) are required. Non-limiting applications that may benefit from the disclosed magnetic core include inductors, transformers, generators, and stators and/or rotors of electric motors (e.g., electric vehicle motors). To provide the above-described anisotropy/directional properties, a predetermined specific magnetic field may be applied while the core is being formed, the magnetic field corresponding to the magnetic flux path in the finished core when used in certain applications. Thus, the applied magnetic field may be tailored for a particular magnetic core application (such as a stator or inductor core). By generating a magnetic field having a shape or path that conforms to, follows, simulates, or approximates the path of the magnetic flux in the end application, the permeability, flux density, and other characteristics can be significantly improved without sacrificing lossy performance. For cores with complex shapes or that experience complex flux paths, the magnetic field may also be complex, e.g. comprising a plurality of different curved or non-linear directional alignments.

The magnetic field may be applied using any suitable method. In at least one embodiment, the alignment fixture may include one or more circuits, each including one or more current carrying wires to generate a magnetic field. By controlling the placement or configuration of the wires and the level and/or direction of the current, a specific customized magnetic field can be generated that mimics or corresponds to the direction of the magnetic flux in the magnetic core during operation. Thus, the magnetic field may align the magnetic particles in multiple directional alignments to conform, simulate, or follow the magnetic flux direction. As used herein, directional alignment may refer to either primary alignment, or alignment that exists on a macro scale as opposed to a micro scale. Thus, small deviations in alignment from one particle to another or between several particles are not considered to be a primary alignment.

In at least another embodiment, the alignment fixture may include one or more magnets for providing a magnetic field during alignment. In one embodiment, the magnet is a permanent magnet. By controlling the placement, configuration, size, shape, and/or strength of the magnets, a particular customized magnetic field can be generated that mimics or corresponds to the direction of magnetic flux in the magnetic core during operation. Although the figures and the following description describe a fixture in which a circuit or magnet is used to generate a magnetic field, one of ordinary skill in the art will appreciate that any combination of the two methods may be utilized. In addition, any magnetic field line or direction shown or described may also be the directional alignment of the magnetic particles.

Referring to fig. 3-15, several examples of fixtures for generating magnetic fields to align magnetic particles in unconsolidated inductor cores, stator cores, and rotor cores are disclosed. These figures and their corresponding description are exemplary, and as noted above, the disclosed methods and fixtures may be applied to form any desired magnetic field for any magnetic flux path. Referring to fig. 3-4, the inductor core 50 is shown as having a hollow rectangular cross-section with an internal cavity. During operation, the magnetic flux 52 in the inductor core is along the periphery of the core 50, as indicated by arrow 54. Although arrow 54 is shown in a clockwise direction, magnetic flux 52 may also be in a counterclockwise direction. To increase the magnetic permeability and magnetic flux density in the core 50, the particles/powders of the core may be aligned in the direction of the flux. As described above, alignment may be provided by applying a magnetic field to the particles/powders during the alignment process and optionally during the pressing and/or sintering or curing process. To generate a magnetic field in the shape or direction of the flux path 52, one or more circuits may be configured to generate a magnetic field. The circuit (not shown) may include one or more current carrying wires 56, the wires 56 being disposed within or about the inductor core 50 and configured to generate a magnetic field 58 in the direction or shape of the magnetic flux path 52.

In one embodiment, shown in fig. 4, magnetic field 58 having the shape of flux path 52 may be generated by placing one or more conductive lines 60 carrying current in one direction inside inductor core 50 and one or more conductive lines 62 carrying current in the opposite direction outside inductor core 50. Fig. 4 shows four wires 60 inside the inductor core 50, however, a single wire 60 may be placed inside (e.g., in the center of) the core 50 to provide a similar magnetic field 58 (similar to fig. 5, described below). Although fig. 3 and 4 show a fixture for an inductor core 50 having a hollow rectangular shape, the inductor core may have any suitable shape, including a ring, a torus, a bar, or other shape. For example, fig. 5 shows an inductor core 50' having a ring shape. Similar to the rectangular core 50 in fig. 3 and 4, the inductor core 50' has a magnetic flux path 52' extending around the periphery of the core 50 '. The flux path 52' may be in a clockwise or counterclockwise direction. To generate a magnetic field 58 'having the shape or direction of the flux path 52', one or more wires 60 carrying current in one direction may be placed inside the core 50 'and one or more wires 62 carrying current in the opposite direction may be placed outside the inductor core 50'. Similar to fig. 4, multiple wires 60, rather than a single wire 60, may be located within the core 50' as shown. The magnetic field 58/58 'may cause the unconsolidated particles to orient themselves to conform to, simulate, or follow the multi-directional alignment 64 of the magnetic field 58/58'. As shown, at least two or more of the alignments 64 may be different from each other. Regardless of the shape of the inductor core, the circuit may be designed to generate a magnetic field corresponding to or simulating the magnetic flux path of the inductor. Similarly, inductor core 50 may be replaced by a transformer core or other magnetic core having a magnetic flux path that would benefit from oriented particles/powders.

Referring to fig. 6-10, additional fixtures for generating a specific customized magnetic field 70 for inductor core 50 are shown, the magnetic field 70 having a shape or direction that mimics or corresponds to magnetic flux 52. The magnetic field 70 may be generated using a fixture that includes a plurality of magnets 72 (e.g., permanent magnets) arranged in a predetermined configuration or pattern. Each magnet 72 may have north (N) and south (S) configurations, and the pattern of magnets 72 may generate a magnetic field 70 that mimics, corresponds to, or approximates the magnetic flux path 52, and correspondingly orient the particles along the magnetic flux path 52. In the embodiment shown in fig. 6, four magnets 72 are arranged inside the inductor core 50 and four magnets are arranged outside the core 50. One magnet is disposed on the inside and outside of each of the four sides of the core 50. The magnets 72 may be arranged such that on the inner and outer sides the magnets alternate between N and S sides/portions of the magnets facing the inductor core 50. In fig. 6, the magnet having the N side/portion facing the inductor core 50 is labeled 74, while the magnet having the S side/portion facing the inductor core 50 is labeled 76. The magnets 72 may be arranged such that magnets 74 having an N-side facing the inductor are positioned opposite each other and magnets 76 having an S-side facing the inductor are positioned opposite each other. As shown in fig. 6, the configuration generates a magnetic field 70 that follows the shape of the perimeter of the inductor core 50. In contrast to the magnetic field 58 in FIG. 4, the magnetic field 70 may not form a complete loop; however, the particle/powder alignment is similar. Fig. 7 shows a Finite Element Analysis (FEA) simulation of the magnet arrangement shown in fig. 6. FEA simulations show that the magnetic field 70 is slightly interrupted (e.g., forms an almost complete loop) along the periphery of the core 50 at the point where the magnet is located. The magnetic field 70 may cause the unconsolidated particles to orient themselves to conform to, simulate, or follow the multi-directional alignment 78 of the magnetic field 70. As shown, at least two or more of the alignments 78 may be different from each other.

As previously described with respect to fig. 5, the inductor core or the transformer core may have any suitable shape, such as a ring, a circular ring or a bar. As shown in fig. 8, a plurality of magnets 72 may also be arranged to produce a desired magnetic field 70' having other core shapes. Similar to the arrangement described with respect to fig. 6, a plurality of magnets 72 may be arranged both inside and outside of the core 50'. The magnets 72 may be arranged such that on the inner and outer sides the magnets alternate between N and S sides/portions of the magnets facing the inductor core 50'. The magnets 72 may be arranged such that magnets 74 having an N-side facing the inductor are positioned opposite each other and magnets 76 having an S-side facing the inductor are positioned opposite each other. As shown in fig. 8, this configuration generates a magnetic field 70', which field 70' is shaped to follow the perimeter of the inductor core 50 '.

While the arrangement of magnets 72 in fig. 6 and 8 is shown with four magnets inside and four magnets outside, with a pair of magnets on each side, such a configuration is exemplary only and not intended to be limiting. The number and/or location of the magnets 72 may be adjusted to adjust the magnetic field to a desired shape/orientation. For example, more magnets 72 may be used to provide a more uniform, complex, and/or refined magnetic field. In the embodiment shown in fig. 9, eight pairs of magnets 72 are arranged in and around the core 50, with two pairs of magnets on each side, to provide a magnetic field 70 ". The magnetic field 70 "may have a shape similar to the magnetic field 70 produced by the arrangement of four pairs of magnets 72 shown in fig. 6, however increasing the number of magnets 72 may provide a more controlled and/or defined magnetic field.

In addition to adjusting the number and/or placement of magnets 72, one or more ferrite cores 80 may be included in the alignment fixture, as shown in fig. 9. For example, the core 82 may be placed in an internal cavity of the inductor core 50 and the other core 84 may be placed outside the core 50. Since the core has a much higher permeability than air, the core can direct the magnetic flux direction. Thus, the core improves the efficiency of the fixture and enhances the magnetic alignment in the magnetic core.

Referring to fig. 10, a plot of magnetization versus field strength in a direction parallel to the alignment of particles in an aligned core and in an isotropic core without particle alignment is shown. The results clearly show that the permeability in the aligned core is much greater than in the misaligned core. The values in fig. 10 are one example and do not necessarily indicate the precise values that may be achieved using the disclosed method and fixture.

Referring to fig. 11-15, the disclosed method and fixture for generating a magnetic field in a magnetic core is also applicable to rotor and stator cores, as well as inductor, transformer, generator, or other magnetic cores. In fig. 11, a fixture for an outside or outer stator core 100 is shown, said core 100 comprising stator teeth 102 and stator slots or gaps 104. The magnetic flux in stator core 100 during operation generally includes a plurality of flux paths that form an arc from one stator tooth 102 to another stator tooth 102 around stator slot 104. Thus, to increase the permeability and flux density along the flux path, a magnetic field 106 may be generated that mimics or approximates the flux path and orients the particles along the flux path 106.

In one embodiment, shown in FIG. 11, the magnetic field 106 may be generated using a fixture that includes one or more circuits. The circuit (not shown) may include one or more current carrying conductors 108. One or more wires 110 may be placed inside the stator slots 104 and one or more wires 112 may be placed outside the stator core opposite the wires 110 inside the stator slots 104. Thus, the fixture may include one or more pairs of wires, with one wire of each pair being inside the stator (e.g., in slot 104) and the other wire of each pair being outside of stator core 100. In one embodiment, one wire 114 in each pair may carry current in one direction and the other wire 116 in each pair carries current in the opposite direction. Pairs of wires may alternate in configuration such that adjacent slots 104 have alternating direction wires, as shown in fig. 11. As a result of the alternating pairs of wires, the magnetic field 106 may be generated such that an arc 118 is formed around the slot 104 from tooth 102 to tooth 102. The magnetic field simulates or approximates the flux path in the stator during operation. The magnetic field 106 may cause the unconsolidated particles to align 122 themselves in multiple directions that conform, mimic, or follow the magnetic field 106 (e.g., an arc shape). As shown, at least two or more of the alignments 122 may be different from each other.

Although fig. 11 is shown with pairs of wires, one inside and one outside of the stator core, in some embodiments, the wires are only inside of the stator core 100 or only outside of the stator core 100. For example, the fixture may include only wires 110 inside stator slots 104. As described above, these wires may alternate the direction of current flow. Additionally, although fig. 11 shows each stator slot 104 including a wire 110, in some embodiments, not every slot 104 may have a wire located therein. Similar to the fixture of inductor core 50 in fig. 9, iron core 120 may be included in the fixture of stator core 100. As shown in fig. 11, the core 120 may be included at the center or inner cavity of the stator core 100. However, the core 120 may also surround the stator 100 in addition to or instead of being centrally placed. Similar to the core in fig. 9, the core 120 may help direct the magnetic flux to form a desired shape or pattern.

Another embodiment of a fixture for providing alignment of magnetic fields 106 in stator core 100 is shown in fig. 12. In this embodiment, one or more wires 110' may be placed adjacent to stator slot 104 or stator tooth 102 rather than inside stator slot 104. In some fixation devices, it may be easier or more convenient to place the wire 110' adjacent to the slot 104. One or more wires 112 may be placed on the outside of the stator core, opposite the wires 110', similar to that described with reference to fig. 11. Also similar to fig. 11, one wire 114 in each pair may carry current in one direction and the other wire 116 in each pair carries current in the opposite direction. The pairs of wires may alternate in their configuration such that the wires 110' have alternating directions, as shown in fig. 12. As a result of the alternating pairs of wires, the magnetic field 106 may be generated such that an arc 118 is formed around the slot 104 from tooth 102 to tooth 102. Similar to the fixture of fig. 11, in some embodiments, there may be wires only inside or outside of stator core 100, and/or not every stator tooth 102 or slot 104 may have wires associated with it.

As described above with respect to fig. 6, 8, and 9, multiple magnets 130 (e.g., permanent magnets) may also be used to provide a particular customized magnetic field. Magnets 130 may be placed or arranged in a fixture to generate magnetic field 132, which magnetic field 132 may have a shape or pattern similar to magnetic field 106 in fig. 11 and 12. In one embodiment shown in fig. 13, a plurality of magnets 130 may be located at a tip or end 134 of each stator tooth 102. Each magnet 130 may have N and S sides or portions, and magnets 130 may be arranged such that they have alternating N and S portions facing stator teeth 102, as shown in fig. 13. In other words, the magnet with the N-side facing the stator teeth 102 may be designated 136 and the magnet with the S-side facing the stator teeth may be designated 138. Each magnet 136 may have a magnet 138 on either side thereof, or vice versa. As described above, the core 140 may be placed in the center or internal cavity of the stator core 100 to assist in directing the magnetic field 132. Although not shown, the fixture may also include a magnet located outside of the stator core, similar to the inductor embodiments described above.

In another embodiment shown in fig. 14, the fixture may include a plurality of magnets 130 disposed within stator slots 104. For example, each stator slot 104 may have a magnet 130 located therein. Magnet 130 may be oriented such that the N-side and S-side each face one side 150 of stator teeth 102. Some magnets 152 may have an N-side facing clockwise and an S-side facing counterclockwise, while other magnets 154 may have an S-side facing clockwise and an N-side facing counterclockwise. In one embodiment, adjacent teeth 102 may have opposing magnet configurations (e.g., 152 or 154) to form an alternating pattern of

magnets

152 and 154, as shown in fig. 14. In other words, each magnet 152 may have a magnet 154 on either side thereof, or vice versa. As shown in fig. 14, the pattern or magnets may generate a magnetic field 132. As described above, the iron core 160 may be placed in the center of the stator core 100 to assist in directing the magnetic field 132. Although not shown, the fixture may also include a magnet located outside of the stator core, similar to the inductor embodiments described above. The magnetic field 132 may cause the unconsolidated particles to orient themselves in a plurality of directional alignments 142 that conform, simulate, or follow the magnetic field 132 (e.g., an arc shape). As shown, at least two or more of the alignments 142 may be different from each other.

Referring to fig. 15, a fixture for orienting the particles/powder of the rotor core 200 is shown. According to the above method, the alignment of the rotor core 200 may be performed using a circuit or a magnet. In the embodiment shown in fig. 15, a magnetic field 202 may be formed using a magnet 204 (e.g., a permanent magnet). The magnets 204 may be grouped into pairs 206, and the pairs 206 may generally form a V-shape or may form an angle (e.g., an obtuse angle). The magnets 204 may each have an N-side and an S-side or portion. In one embodiment, each pair of magnets 206 may be configured such that both magnets 204 have the same side (N or S) facing outward. The N-side outward pair of magnets 206 may be designated 208 and the S-side outward pair of magnets 206 may be designated 210. In one embodiment, the pairs may alternate such that each pair 208 has a pair 210 on each side, and vice versa, as shown in FIG. 15. Although fig. 15 shows four pairs of magnets 206, two pairs 208 and two pairs 210, the fixture may include any suitable number of pairs 206 of magnets 204. The magnetic field 202 may cause the unconsolidated particles to orient themselves to conform to, simulate, or follow the multi-directional alignment 212 of the magnetic field 202. As shown, at least two or more of the alignments 212 may be different from each other.

In at least one embodiment, the magnets 204 used in the fixture may be the same permanent magnets that are incorporated into the rotor core 200 in their final form (e.g., in a permanent magnet motor). Thus, the permanent magnets used in the rotor are also used to orient the particles/powder in the rotor core manufacturing process (e.g., alignment and optional compaction and/or sintering/solidification). The permanent magnets may be embedded in the powder core during the manufacturing process and may remain in the core after machining is complete to form the final rotor core. Similar to the above-described fixtures, fixtures for rotor orientation may include a core 214, which core 214 surrounds (partially or completely) rotor core 200 to help direct magnetic field 202.

Non-limiting examples of the fixtures depicted in fig. 3-15 have been described in the context of sintered or bonded magnets. By applying the disclosed magnetic field using a fixture when the magnetic powder is not fully consolidated, the orientation of the particles can be made easier and more efficient. However, the disclosed fixtures may also be used to orient consolidated or fully formed magnets, such as those formed from electrical steel (e.g., electrical steel laminations). To more effectively orient the magnetic particles, the magnetic core may be heated to a temperature of, for example, 400 ℃ to 900 ℃. Heating can be accomplished using any suitable method, and a heating device can be added to any of the disclosed fixtures. Thus, the disclosed advantages of the above-described orientation of the magnetic particles can be achieved in magnetic cores that are not formed from magnetic powder or that have been consolidated.

While exemplary embodiments are described above, these embodiments are not intended to describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. In addition, features of the various implemented embodiments may be combined to form further embodiments of the invention.

According to the present invention, a method for forming an aligned permanent magnet includes mixing or coating a rare earth magnetic powder with an electrically insulating material; consolidating the powder to form a consolidated powder; applying a magnetic field to the consolidated powder to align particles of the consolidated powder and form an aligned powder; and sintering the aligned powders to form the aligned permanent magnet.

According to one embodiment, the above invention is further characterized by pressing the aligned powders.

According to one embodiment, said consolidating comprises a compaction process.

According to one embodiment, the above invention is further characterized by heating the consolidated powder during said applying.

According to one embodiment, the heating element comprises induction heating.

According to one embodiment, the heating is performed until a main phase curie temperature is achieved.

According to one embodiment, the curie temperature of the main phase is lower than the melting point of the main phase.

According to one embodiment, the consolidated powder is contained in an electrically conductive container, further comprising applying an electrical current to the electrically conductive container.

According to one embodiment, the heating comprises placing the consolidated powder in a current-carrying coil for generating an alternating magnetic field with eddy currents to generate heat.

According to the present invention, a method for forming an aligned permanent magnet includes consolidating a rare earth magnetic powder to form a consolidated powder; applying a magnetic field to the consolidated powder to align particles of the consolidated powder; heating the consolidated powder to a major phase curie temperature of the rare earth magnetic powder to form an aligned powder during the applying; and sintering the aligned powders to form the aligned permanent magnet.

According to one embodiment, said consolidating comprises a compaction process.

According to one embodiment, the above invention is also characterized in that the rare earth magnetic powder is prepared by mixing or coating a rare earth magnetic material with an electrically insulating material.

According to one embodiment, the above invention is further characterized by placing the rare earth magnetic powder in a coil configured to carry a high frequency current of 5kHz to 500 kHz.

According to one embodiment, the heating comprises generating eddy currents from an alternating magnetic field from the coil.

According to one embodiment, a rare earth magnetic powder is contained in a container having at least one electrically conductive surface.

According to one embodiment, at least a portion of the container comprises an insulating material.

According to the present invention, a method for forming an aligned permanent magnet includes consolidating a rare earth magnetic powder to form a consolidated powder; applying a magnetic field to the consolidated powder to align particles of the consolidated powder; applying an electric current in the presence of the magnetic field to heat the consolidated powder to a major phase curie temperature; and after the applying, sintering the consolidated powder to form the aligned permanent magnets.

According to one embodiment, the heating comprises containing the rare earth magnetic powder in an electrically conductive container such that the current inductively heats the electrically conductive container.

According to one embodiment, the heating includes placing the rare earth magnetic powder in a coil, and generating an alternating magnetic field from an electric current having an eddy current to generate heat.

Claims

1. A method of forming an aligned permanent magnet, the method comprising:

mixing or coating a rare earth magnetic powder with an electrically insulating material;

consolidating the powder to form a consolidated powder;

applying a magnetic field to the consolidated powder to align its particles and form an aligned powder; and

sintering the aligned powders to form the aligned permanent magnets.

2. The method of claim 1, further comprising pressing the aligned powder.

3. The method of claim 1, wherein the consolidating comprises a compaction process.

4. The method of claim 1, further comprising heating the consolidated powder during the applying.

5. The method of claim 4, wherein the heating comprises induction heating.

6. The method of claim 4, wherein the heating is performed until a main phase Curie temperature is achieved.

7. The method of claim 6, wherein the principal phase Curie temperature is below the principal phase melting point.

8. The method of claim 4, wherein the consolidated powder is contained in an electrically conductive container, the method further comprising applying an electrical current to the electrically conductive container.

9. The method of claim 4, wherein the heating comprises placing the consolidated powder in a current-carrying coil for generating an alternating magnetic field having eddy currents to generate heat.

10. A method of forming an aligned permanent magnet, the method comprising:

consolidating the rare earth magnetic powder to form a consolidated powder;

applying a magnetic field to the consolidated powder to align its particles;

heating the consolidated powder to a major phase curie temperature of the rare earth magnetic powder during the applying to form an aligned powder; and

sintering the aligned powders to form the aligned permanent magnets.

11. The method of claim 10, wherein the consolidating comprises a compaction process.

12. The method of claim 10, wherein the principal phase curie temperature is below the principal phase melting point.

13. The method of claim 10, further comprising preparing the rare earth magnetic powder by mixing or coating a rare earth magnetic material with an electrically insulating material.

14. The method of claim 10, further comprising placing the rare earth magnetic powder in a coil configured to carry a high frequency current of 5kHz to 500 kHz.

15. The method of claim 14, wherein the heating comprises generating eddy currents from an alternating magnetic field from the coil.