Brushless electric machine and method for manufacturing a brushless electric machine

Abstract

The invention relates to a brushless electric machine (10), in particular a brushless DC motor (12), with a stator (14) and a rotor (18) arranged rotatably within the stator (14) relative to it, wherein the rotor (18) has a cylindrical base body (20) which is non-rotatably connected to a machine shaft (16) and carries a plurality of permanent magnets (24) on its outer circumference (22), and wherein the stator (14) has a stator winding (32) with a plurality of single-tooth windings (28) for driving the rotor (18) by means of an electrically generated rotating magnetic field. It is proposed that the permanent magnets (24) of the rotor (18) are fixed by means of a thin-walled reinforcement (56) radially surrounding them, wherein the reinforcement (56) has a modulus of elasticity of at least 150 GPa and / or a yield strength of at least 600 MPa. Furthermore, the invention relates to a method for manufacturing the brushless electric machine (10).

Description

[0001] The invention relates to a brushless electric machine, in particular a brushless DC motor, with a stator and a rotor arranged within the stator so as to be rotatable relative thereto according to the preamble of independent claim 1, wherein the rotor has a cylindrical base body which is non-rotatably connected to a machine shaft and carries a plurality of permanent magnets on its outer circumference, and wherein the stator has a stator winding with a plurality of single-tooth windings for driving the rotor by means of an electrically generated rotating magnetic field. State of the art

[0002] A brushless electric machine is understood to be, in particular, an electric machine with a stator-side three-phase winding that can be controlled or regulated in such a way as to generate a rotating magnetic field which drives a permanent magnet rotor. Alternatively, it is also conceivable to use the rotor in conjunction with a generator.

[0003] Rotors for brushless electric machines, especially brushless DC machines – abbreviated BLDC (brushless direct current) or EC (electronically commutated) machines – with permanent magnets are generally manufactured in two different designs. Firstly, the permanent magnets of different polarities can be embedded in so-called pockets within a cylindrical base body. Secondly, the magnets, or a correspondingly polarized magnetic ring, can be applied externally to the base body as surface magnets. The base body usually consists of numerous rotor laminations stacked to form a rotor core, each lamination being stamped from a soft magnetic sheet. However, other designs for rotors for electric machines, particularly for EC machines, are also conceivable.The cylindrical base of the rotor, for example, can be constructed from composite materials (Soft Magnetic Composites - SMC). SMC materials consist of high-purity iron powder with a special surface coating on each individual particle. This electrically insulating surface ensures high electrical resistance even after pressing and heat treatment, which in turn minimizes or eliminates eddy current losses. SMC materials are well-known to those skilled in the art, so their composition will not be discussed further here.

[0004] The permanent magnets of the magnetic ring consist in particular of a hard magnetic material, for example, an iron, cobalt, or nickel alloy. If the permanent magnets are designed as surface magnets, they can be magnetized either before or after mounting on the rotor. Alternatively, polymer-bonded permanent magnets are conceivable, the magnetic powder of which is embedded in a matrix of polymer binder. The magnetic powder can consist, for example, of hard ferrite, SmCo, and / or NdFeB, or be an AlNiCo alloy. Preferably, the polymer binder is a thermoplastic binder, for example, made of polyamide or polyphenylene sulfide. Alternatively, it is also conceivable that the polymer binder is a thermosetting binder, for example, an epoxy resin.

[0005] Surface magnets, despite their numerous advantages over buried magnets, have the disadvantage of lower mechanical strength against centrifugal forces acting on them during the operation of the electric motor. To prevent defects and failures, the way the surface magnets are mounted to the base body is therefore just as important as their mechanical strength.

[0006] From DE 11 2016 0004 207 T5, a rotor for an electric machine is known, comprising a rotor core, a plurality of permanent magnets, a conductive element, and a retaining element. The permanent magnets are formed on an outer peripheral region of the rotor core and arranged circumferentially spaced apart from one another by means of pole gaps. The conductive element has a conductivity higher than that of the permanent magnets. It surrounds the rotor core and the plurality of permanent magnets as a whole and has first and second opposing regions that are circumferentially separated by a gap. Finally, the retaining element surrounds the rotor core, the plurality of permanent magnets, and the conductive element as a whole.

[0007] The object of the invention is to provide a brushless electric machine in which the permanent magnets arranged on the outer circumference of the rotor are held with an improved reinforcement compared to the prior art, which affects the magnetic flux between stator and rotor as little as possible. Advantages of the invention

[0008] To solve the given problem, the rotor's permanent magnets are fixed by means of a thin-walled reinforcement radially surrounding them. This reinforcement has a modulus of elasticity of at least 150 GPa (gigapascals) and / or a yield strength of at least 600 MPa (megapascals). This offers the particular advantage of securely fixing the permanent magnets even at very high speeds of the brushless electric motor exceeding 20,000 rpm (rotations per minute), while simultaneously minimizing the magnetic gap between the rotor and stator to increase the electric motor's efficiency. A high modulus of elasticity results in very low deformation despite the reinforcement's thin wall thickness. A high yield strength prevents plastic deformation at the outer circumference of the reinforcement, even during short-term tests at twice the rotor's maximum speed.

[0009] The invention further relates to an electrically driven machining device, in particular an electric hand-held power tool, comprising the brushless electric motor according to the invention. In the context of the invention, an electrically driven machining device is understood to include, among other things, battery-powered and / or mains-powered machine tools for machining workpieces using an insert tool driven by a brushless electric motor. The electric machining device can be designed as either a hand-held or stationary machine tool. Typical machine tools in this context are hand-held or bench drills, screwdrivers, impact drills, planers, angle grinders, orbital sanders, polishing machines, or the like.However, suitable electrical appliances also include appropriately powered garden and construction equipment such as lawnmowers, string trimmers, pruning saws, rotary tillers and trenchers, blowers, robotic breakers and excavators, or the like. Furthermore, the invention is applicable to brushless electric motors in household appliances such as vacuum cleaners, blenders, etc.

[0010] In a further embodiment, the reinforcement is provided for in a paramagnetic metal, in particular aluminum, brass, stainless steel, or the like. Alternatively, the reinforcement can also consist of a plastic with a permeability of no more than 15, in particular no more than 2, or of a composite material formed from the plastic and the paramagnetic metal. Paramagnetic metals are defined as metals whose permeability is greater than 1, which are not strongly attracted to a magnet, and which are themselves not magnetizable. Paramagnetic metals thus differ significantly in their magnetic properties from ferromagnetic metals, such as iron, and diamagnetic metals, such as copper. It should be noted here that the term "amagnetic" is occasionally also used for paramagnetic or non-ferromagnetic materials.Strictly speaking, there are no truly non-magnetic materials, as every material becomes magnetic above a certain intensity of magnetic field to which it is exposed. A particularly advantageous feature is the prevention of a partial or complete short circuit in the magnetic circuit of a brushless electric motor, thanks to a reinforcement made of a paramagnetic metal and / or a plastic with a low permeability.

[0011] The reinforcement is designed as at least one hollow cylindrical sleeve, which is positively connected to the permanent magnets by means of a longitudinal press fit. This enables particularly simple manufacturing of the brushless electric motor, since the at least one sleeve for the longitudinal press fit can be slid onto the rotor's permanent magnets along a longitudinal axis of the machine shaft. During the longitudinal press fit, the at least one sleeve is plastically and irreversibly deformed by an expansion of its inner diameter.

[0012] At least one sleeve can be provided with a seam that runs essentially perpendicular to the longitudinal axis of the machine shaft of the brushless DC machine. Unlike a seamless sleeve, a seam allows for a simpler manufacturing process. The armoring can also consist of multiple sleeves that are slid onto the permanent magnets. The individual sleeves of the armoring can be slid onto the permanent magnets mounted on the rotor sequentially from one direction or, particularly in the case of an even number of sleeves, in pairs from both directions along the longitudinal axis of the machine shaft.

[0013] A simplified sliding on of at least one sleeve is made particularly advantageous by the fact that it has an insertion phase at an open end which widens relative to its inner diameter, the inner diameter of which is larger than an outer diameter of the rotor with the mounted permanent magnets. Examples of implementation Drawing

[0014] The invention is described below with reference to the Fig. Figures 1 to 11 are explained by way of example, whereby identical reference symbols in the figures indicate identical components with the same function. They show Fig. 1: A cross-sectional view of a three-phase, brushless electric machine according to the state of the art, Fig. 2: a block diagram of an electronic circuit for controlling the electric machine designed as a brushless DC motor according to Fig. 1, Fig. 3: A first embodiment of the brushless electric motor according to the invention in a sectional view, Fig. 4: A second embodiment of the rotor of the brushless electric machine according to the invention in a perspective view, Fig. 5: a section through the sleeve according to the invention for fixing the permanent magnets of the rotor according to Fig. 4, Fig. 6: A third embodiment of the rotor of the brushless electric machine according to the invention in a perspective view, Fig. 7: A first embodiment for connecting the sleeve according to the invention with the permanent magnets in a perspective view, Fig. 8: an embodiment of a single weld point according to Fig. 7 in a top view, Fig. 9: a second embodiment for connecting the sleeve according to the invention with the permanent magnets in a perspective view, Fig. 10: a third embodiment for connecting the sleeve according to the invention with the permanent magnets in a perspective view and Fig. 11: A fourth embodiment for connecting the sleeve according to the invention with the permanent magnets in a perspective view. Description of the exemplary implementations

[0015] Fig. Figure 1 shows a cross-section through a prior art brushless electric machine 10, designed as a three-phase brushless DC motor (BLDC or EC motor) 12 with a stator 14 and a rotor 18 fixedly mounted on a machine shaft 16. The brushless DC motor 12 serves to drive a machine tool (not shown in detail), such as a vacuum cleaner, a machine tool, or the like. Instead of a BLDC or EC motor 12, an alternating current motor (AC motor), for example, an asynchronous or synchronous motor, could also be used. The rotor 18 of the brushless DC motor 12 comprises a cylindrical base body 20, which has a plurality of permanent magnets 24 on its outer circumference 22. These permanent magnets are designed as surface magnets and alternate in their polarity N, S in the circumferential direction of the rotor 18.In the exemplary embodiment, four permanent magnets 24 are shown, which in turn form two rotor pole pairs. However, a different number of permanent magnets 24 is also conceivable. The stator 14 has six radially inwardly directed stator teeth 26, each of which carries a single-tooth winding 28, with each pair of opposing single-tooth windings 28 forming a winding strand 30 of a three-phase stator winding 32. The stator 14, with its stator teeth 26, defines a cylindrical cavity in which the rotor 18 is rotatably arranged relative to the stator 14 by means of the machine shaft 16. When current flows, the winding strands 30 generate a rotating magnetic field, which sets the permanently excited rotor 18 and the machine shaft 16 into rotational motion. It should be noted for the avoidance of doubt that the following invention is not only applicable to a brushless electric machine 10 designed as an electric motor.Likewise, the brushless electric machine 10 can also be configured as a generator of a corresponding design. However, the invention will be described below only with reference to the brushless DC motor 12.

[0016] In Fig. 2 is a device 34 for controlling the brushless DC motor 12 according to Fig. Figure 1 shows the device 34. Besides the brushless DC motor 12, the device 34 comprises a control unit 36, a driver circuit 38, and a comparator 40. For clarity, only the most important components and assemblies of the device 34 are shown. The control unit 36 ​​can be a microprocessor (µP), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), or the like. It is also conceivable that the control unit 36 ​​consists at least partially of discrete semiconductor components. The driver circuit 38 is designed as an inverter in the form of a B6 bridge circuit and has a half-bridge 42 configured as an inverter circuit for each phase or winding 30 of the three phases U, V, W of the stator winding 32. Each half-bridge 42 consists of a first power switch 44, which is connected to a high supply potential V. H(High Side) is connected, and a second circuit breaker 46, which is connected to a low supply potential V L (Low Side) is connected. The power switches 44, 46 can be designed as semiconductor switches in the form of IGBTs, IGCTs, thyristors, power MOSFETs or the like, or as relays. The control unit 36 ​​controls the individual power switches 44, 46 to energize two winding strands 30 each by means of a pulse-width modulated signal or a plurality of pulse-width modulated signals S PWM(both terms are used synonymously here) such that the first circuit breaker 44 of one of the three half-bridges 42 is closed (e.g., T1), while the first circuit breakers 44 of the other two half-bridges 42 are open (e.g., T3 and T5), and that at least the second circuit breaker 46 of one of the other two half-bridges 42 is closed (e.g., T2), while the second circuit breaker 46 of at least that half-bridge 42 (e.g., T4) whose first circuit breaker 44 (e.g., T1) is closed is open. In this way, to generate the rotating magnetic field, the first circuit breakers 44 and the second circuit breakers 46 can be alternately switched such that four of the six individual tooth windings 28 of the winding strands 30 are energized, so that during operation the resulting stator magnetomotive force is on average oriented perpendicular to the rotor magnetomotive force.Furthermore, to prevent short circuits, it is ensured that both circuit breakers 44 and 46 of the same half-bridge 42 are never closed simultaneously (e.g., T1 and T4). For this purpose, the circuit breakers 44 and 46 of the same half-bridge 42 are always closed with a certain dead time after the opening of the other circuit breaker 44 and 46 by means of the pulse-width modulated signal S. PWM Closed. This type of circuit is familiar to experts, so it will not be discussed further here. Instead of multiple B6 half-bridges, H-bridges or comparable inverter circuits can also be used to control the individual phases U, V, W of the brushless DC motor 12.

[0017] To determine the precise switching times for the individual power switches 44, 46 of the driver circuit 38, the control unit 36 ​​must know the position of the rotor 18. The rotor position can be determined, for example, using sensors, such as Hall sensors, arranged around the circumference of the rotor 18 on the stator 14. However, instead of sensor-based rotor position determination, it is often advantageous to determine the position sensorlessly via back EMF in conjunction with electrical commutation. This generally results in lower costs due to the elimination of sensors, as well as greater reliability and a more compact design for the brushless electric machine 10. When using back EMF, the voltage induced in a de-energized winding 28 by the permanent magnets 24 of the rotor 18 is detected.According to the state of the art, this is done by first determining the zero crossing of a phase current I. U , I V , I W one of the phases U, V, W is predicted and the current flow to the corresponding winding 30 for a predetermined time period, in which the predicted zero crossing lies, is controlled by means of the pulse width modulated signal S PWM interrupted. After the phase voltage U is switched off U , U V , U W The corresponding phase current I flows through the respective phase U, V, W. U , I V , I W via a freewheeling element (not shown) connected in parallel to the switched-off power switch 44, 46. In the case of a MOSFET, the freewheeling element is implemented, for example, by its intrinsic freewheeling diode. Since the freewheeling diode conducts only in one direction, a sudden increase in voltage occurs as soon as the phase current I U , I V , I WThe value zero is reached by the relevant winding strand 30. Thus, the zero crossing of the strand current I can be determined. U , I V , I U after switching off the phase voltage U U , U U , U W determined and the phase shift between phase current I U , I V , I W and back-EMF to determine the position of rotor 18.

[0018] In the illustrated embodiment according to Fig. 2. Only phase U is used to determine the rotor position. Comparator 40 calculates an arithmetic difference U for this purpose. Diff between a potential V applied to a first input SP a common star point 48 of the winding strands 30 of the brushless DC motor 12 and a potential V applied to a second input BF,U a node 50 for energizing the respective winding strand 30 of phase U. To determine the potential VBF,U The voltage induced in the unenergized winding strand 30 is a voltage divider 54 formed from at least two resistors 52, which is connected on one side to the node 50 and on the other side to a reference potential V GND , the low supply potential V L or a comparable reference potential. The arithmetic difference U Diff This is then converted into a digitized back-EMF signal S BF,U from comparator 40 to control unit 36.

[0019] Fig. Figure 3 shows the invention by means of a section through the brushless DC motor 12 transverse to the longitudinal axis A of the machine shaft 16. Accordingly Fig. 1. The base body 20 of the rotor 18, which is rotationally fixed to the machine shaft 16, carries permanent magnets 24 with alternating polarities N, S on its outer circumference 22. The permanent magnets 24 are connected to the base body 20 by material, form, and / or force-fit connections and are also fixed by means of a thin-walled reinforcement 56 radially surrounding them. To ensure that the permanent magnets 24 are securely fixed even at very high speeds of the brushless DC motor 12 exceeding 20,000 rpm, and to minimize the magnetic gap between the rotor 18 and stator 14 for maintaining or increasing efficiency, the reinforcement 56 has a modulus of elasticity of at least 150 GPa and / or a yield strength of at least 600 MPa.In this way, a high modulus of elasticity can cause very little deformation despite the small wall thickness, while a high yield strength prevents unwanted plastic deformation on an outer circumference 58 of the reinforcement 56.

[0020] To prevent a partial or complete short circuit of the magnetic circuit of the brushless electric motor 12, the armor 56 is made of a paramagnetic metal, in particular aluminum, brass, stainless steel, or the like. Alternatively, the armor 56 can also be made of a plastic with a permeability of µ. r of a maximum of 15, in particular of a maximum of 2, or consisting of a composite material made of the plastic and the paramagnetic metal.

[0021] A pole gap 60 is provided between each pair of adjacent permanent magnets 24 mounted on the base body 20 of the rotor 18. For the positive-locking or force-locking attachment of the permanent magnets 24, the base body 20 of the rotor 18 has projections 62 distributed around its outer circumference 22, by means of which the preferably still unmagnetized permanent magnets 24 can be positioned with the defined pole gaps 60. These projections 58 can, for example, be designed as knobs, ridges, or the like on the base body 20. Alternatively or additionally, the permanent magnets 24 can also be bonded to the base body 20, for example, by means of adhesive bonding. The pole gaps 60 allow for optimization both with regard to the power density of the brushless DC motor 12 and with regard to the utilization of the magnetic material used for the permanent magnets 24.Depending on requirements, a compromise between the cost and efficiency of the brushless DC motor 12 can be easily achieved by keeping the pole gaps 60 as small as possible to avoid or minimize the reduction in power density of the brushless DC motor 12, while simultaneously making them large enough to maximize the utilization of the magnet material. The ratio between the circumferential width W of the pole gap 60 and the outer diameter D is... R of the rotor 18 equipped with the permanent magnets 24 (see also Fig. 4) preferably less than 10%. In this context, a thin-walled reinforcement 56 is preferably understood to mean that a thickness T of the reinforcement 56 is less than 2% of its inner diameter D. I amounts.

[0022] To manufacture the brushless DC motor 12 according to the invention, in a first process step a plurality of initially unmagnetized or weakly magnetized permanent magnets 24 are mounted on the outer circumference 22 of the base body 20 of the rotor 18, particularly by means of a mounting device (not shown in detail), such that a pole gap 60 remains between each pair of adjacent permanent magnets 24. The permanent magnets 24 can be attached to the base body in the manner described above by means of a material-fit, form-fit, and / or force-fit connection. In a subsequent process step, the reinforcement 56 is pushed onto the permanent magnets 24 of the rotor 18 in the direction of the longitudinal axis A of the machine shaft 16. This can also preferably be automated by the mounting device.During the sliding process, the reinforcement 56 is connected to the permanent magnets 24 via a force-fit longitudinal press connection such that the reinforcement 56 expands its inner diameter D. I (cf.) Fig. 5) is plastically and irreversibly deformed. Before the rotor 18 is inserted into the stator 14, the permanent magnets 56 are magnetized in a further process step by means of at least one magnetizing coil of the assembly device.

[0023] The pole gaps 60 between two adjacent permanent magnets 24 offer the advantage of simple, subsequent, and, above all, complete magnetization of the initially unmagnetized or weakly magnetized permanent magnets 24. Complete magnetization results in a significantly higher magnetic flux, so that the permanent magnets 24 also make a considerable contribution to torque generation in the brushless DC motor 12, even at their edges. Furthermore, the unmagnetized or weakly magnetized permanent magnets 24 can be positioned more easily and precisely around the outer circumference 22 of the rotor body 20, since they exhibit no or only a weak magnetic attraction.

[0024] Fig. Figure 4 shows a further embodiment of the rotor 18 in a perspective view. The reinforcement 56 is designed as a hollow cylindrical sleeve 64, which is positively connected to the permanent magnets 24 of the rotor 18 by means of a longitudinal press fit. During the longitudinal press fit, the sleeve 64 expands by means of an expansion of its inner diameter D. I Plastically and irreversibly deformed. While the reinforcement 56 according to Fig. While the sleeve 64 can, for example, also be designed as a ring extending only over part of the length of the base body 20 of the rotor 18, it completely encloses the permanent magnets 24. The sleeve 64 thus extends along the entire length of the base body 20 of the rotor 18 in the direction of the longitudinal axis A of the machine shaft 16. At an open end 66, the sleeve 64 has a diameter that is different from its inner diameter D. I widening insertion phase 68, whose inner diameter D Pis larger than an outer diameter D R of the rotor 18 with the mounted permanent magnets 24. This allows for a simplified sliding of the sleeve 64 along the longitudinal axis A of the machine shaft 16.

[0025] For clarification, the thin-walled sleeve 64 of thickness T, which has not yet been pushed onto the rotor 18, is shown in Fig. Figure 5 shows a section along the longitudinal axis A. It can be seen that the inner diameter D P The insertion phase 68 at the open end 66 of the sleeve 64 is larger than the inner diameter D I its hollow cylindrical part. To achieve the longitudinal press fit during the sliding on of the sleeve 64, the inner diameter D must be I the hollow cylindrical part of its uninserted state must be smaller than the outer diameter D Rof the base body 20 of the rotor 18, which is equipped with the permanent magnets 24. Thus, in the reassembled state of the sleeve 64, the following relationship D applies. P > D R > D I Furthermore, a sufficiently high yield strength of at least 600 MPa for the sleeve 64 prevents unwanted plastic deformation at its outer circumference 58 during operation of the brushless DC motor 12. This allows, firstly, a very small magnetic gap between rotor 18 and stator 14 without the risk of mechanical contact and, secondly, ensures the concentricity of the rotor 18 even at very high speeds.

[0026] Fig. Figure 6 shows a further embodiment of the invention, wherein the reinforcement 56 is formed from two sleeves 64', 64" which are joined by means of a seam 70 running substantially perpendicular to the longitudinal axis A of the machine shaft 16. In contrast to the seamless sleeve 64 according to the Fig. 4 and Fig. The seam 70 allows for a simpler manufacturing and assembly process of the sleeves 64', 64" in particular when the rotor 18 has a particularly long base body 20. The sleeves 64', 64" can be joined, in particular welded, by means of the seam 70 before being slid onto the permanent magnets 24, such that after joining they each have an insertion phase 68', 68" at their open ends 66', 66". Alternatively, it is also conceivable that the individual sleeves 64', 64" of the reinforcement 56 are slid one after the other from one direction or, in particular in the case of an even number of sleeves 64, in pairs from both directions along the longitudinal axis A of the machine shaft 16 onto the permanent magnets 24 mounted on the rotor 18 base body 20 and subsequently joined by means of the seam 70.If the sleeves 64', 64" are made of a plastic or composite material, the seam 70 connecting them can also be produced by laser welding or similar methods. Bonding of the seam 70 is also conceivable.

[0027] Fig. Figure 7 shows a first embodiment for connecting the reinforcement 56, designed as a sleeve 64, to the permanent magnets 24 in a perspective view. For illustrative purposes, the base body 20 and the machine shaft 16 of the rotor 18 have been omitted. However, it should be noted that the permanent magnets 24 – as described above – are already mounted on the base body 20 of the rotor 18 before the sleeve 64 is slid onto it, maintaining the bobbin gaps 60 provided between them. The sleeve 64, which is made of a paramagnetic metal, is connected to the permanent magnets 24 by means of a plurality of weld points 72, forming a material-locking and / or form-locking connection. The weld points 72 can be applied particularly advantageously after the sleeve 64 has been slid onto the permanent magnets 24, automatically using a suitable welding device, in particular a laser, which is not shown in detail.Manual placement of the weld points 72 is also conceivable. This allows the brushless DC motor 12 in general, and its rotor 18 in particular, to be protected efficiently and cost-effectively against damage, for example, by deformation and / or axial displacement of the sleeve 64 along the longitudinal axis A of the machine shaft 16, even at very high speeds of more than 20,000 rpm, as well as in the event of impacts, falls, or the like.

[0028] Depending on the operating parameters of the brushless DC motor 12 and / or the sleeve 64, the number, shape, and distribution of the weld points can vary. For example, the number of weld points 72 should be as large as possible or as small as necessary to securely fix the sleeve 64, while simultaneously minimizing the number of weld points 72 or minimizing the number of weld points 72 to avoid impairing the magnetic flux between the rotor 18 and the stator 14. According to Fig. In the area of ​​the pole gaps 60, three weld points 72 are provided along the longitudinal axis A – two of the weld points 72 near the open ends 66 and a third essentially at half the length of the sleeve 64. In the case of a longer or shorter sleeve 64, correspondingly more or fewer weld points 72 may be provided. The number of weld points 72 also depends on the outer diameter D. R Depending on the dimensions of the rotor 18 and the number of permanent magnets 24 or pole gaps 60, it is possible not to place the weld points 72 near every pole gap 60, but rather to omit individual pole gaps 60. However, it is advantageous if the number of weld points 72 per permanent magnet 24 is in the range of 1 to 10, in particular from 2 to 4, whereby this – as mentioned – depends significantly on the dimensions of the rotor 18 as well as the number, size and shape of the permanent magnets 24.

[0029] Fig. Figure 8 shows a single weld point 72 in a top view. In addition to a material-bonded connection, a form-fit connection can also be created using the laser by briefly heating a focal point intensely, creating a molten column that softens or liquefies parts of the sleeve 64 and the permanent magnet 24. After the molten column solidifies, an undercut and / or a protrusion forms between the sleeve 64 and the permanent magnet 24, resulting in the form fit. Besides optimizing the number of weld points 72, their size or shape can alternatively or additionally be varied so that each has a diameter D. SThe sleeve 64 and the permanent magnets 24 must have a thickness of approximately 0.2 to 2 mm. Both the sleeve 64 and the permanent magnets 24 must be made of suitable weldable materials to ensure a metallurgical bond. For the sleeve 64, this is primarily achieved by using a paramagnetic metal, although plastics and composite materials also exist that are suitable for welding to the permanent magnets 24. The material of the permanent magnets 24 should preferably be sintered or hot-pressed. However, plastic-bonded permanent magnets 24 can also be used. The same applies to any coatings on the sleeves 64 and the permanent magnets 24. The number, shape, and distribution of the weld points 72 can, among other things, compensate to a limited extent for any imbalance of the rotor 18, so that the weld points 72 do not necessarily have to be arranged symmetrically around the outer circumference 58 of the sleeve 64.

[0030] In Fig. Figure 9 shows a second embodiment for the material-locking and / or form-locking connection of the sleeve 64 and the permanent magnets 24 by means of a plurality of weld points 72 in a perspective view. In contrast to Fig. In section 8, two weld points 72 are arranged along the longitudinal axis A, essentially circumferentially, of the sleeve 64, centrally above each permanent magnet 24. The weld points 72 are located near the two open ends 66 of the sleeve 64. However, it is also conceivable that more weld points could be arranged along the longitudinal axis A, depending on the length of the sleeve 64. It is also conceivable that with a smaller outer diameter D R not every permanent magnet 24 of the rotor 18 is connected to the sleeve 64 by means of a form-fit and / or force-fit connection via the weld points 72.

[0031] A third embodiment for connecting the sleeve 64 and the permanent magnets 24 by means of a plurality of weld points 72 is shown. Fig. 10. Four welding points 72 are provided for each permanent magnet 24 such that they are located near the two open ends 66 of the sleeve 64 in edge areas of the permanent magnets 24 near the pole gaps 60.

[0032] Fig. Figure 11 shows a fourth embodiment for connecting the sleeve 64 and the permanent magnets 24. After the sleeve 64 has been slid onto the sleeve, a ring 74 is attached to one of its open ends 66, in particular to the open end 66 opposite the open end 66 with the insertion phase 68, such that it is metallurgically bonded to the permanent magnets 24 at its end face and to the sleeve 64 at its circumferential edge 76 via a plurality of spot welds 72. One spot weld 72 can be provided on the permanent magnet 24. However, depending on the outer diameter D, the number of spots welded 72 is also determined. RThe number of weld points 72 on the rotor 18 and the number of permanent magnets 24 can also vary. Preferably, the ring 74 is made of the same material as the sleeve 64. It is also possible to provide a ring 74 at each open end 66 of the sleeve 64. Instead of a ring 74, the sleeve 64 can also have individual tabs at at least one of its open ends 66, which are bent over after being slid onto the permanent magnets 24 and welded to the end face of the permanent magnet 24.

[0033] Finally, it should be noted that the invention does not apply to the inventions described in the Fig.The embodiments shown in Figures 3 to 11 are not limited to these examples, but are to be understood as illustrative. In particular, the number, shape, and size of the permanent magnets 24 can vary. The size of the rotor 18 and the design of the stator 14 of the brushless DC motor 12 shown in the figures are also not to be understood as limiting. This also applies to the brushless DC motor 12 and the electronics controlling it, which would have to be adapted accordingly in the case of a brushless electric machine 10 designed as a generator. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 11 2016 0004 207 T5

[0006]

Claims

[1] Brushless electric machine (10), in particular a brushless DC motor (12), with a stator (14) and a rotor (18) arranged within the stator (14) so ​​as to be rotatable relative thereto, wherein the rotor (18) has a cylindrical base body (20) which is connected in a rotationally fixed manner to a machine shaft (16) and carries a plurality of permanent magnets (24) on its outer circumference (22), and wherein the stator (14) has a stator winding (32) with a plurality of single-tooth windings (28) for driving the rotor (18) by means of an electrically generated rotating magnetic field, characterized by that the permanent magnets (24) of the rotor (18) are fixed by means of a thin-walled reinforcement (56) radially surrounding them, wherein the reinforcement (56) has a modulus of elasticity of at least 150 GPa and / or a yield strength of at least 600 MPa. [2] Brushless electric machine (10) according to claim 1, characterized bythat the reinforcement (56) consists of a paramagnetic metal, in particular aluminum, brass, stainless steel or the like. [3] Brushless electric machine (10) according to claim 1, characterized by that the reinforcement (56) is made of a plastic with a permeability number (µ r ) of a maximum of 15, in particular of a maximum of 2, or of a composite material formed from the plastic and a paramagnetic metal, in particular aluminium, brass, stainless steel or the like. [4] Brushless electric machine (10) according to one of the preceding claims, characterized by that the reinforcement (56) is designed as at least one hollow cylindrical sleeve (64, 64', 64") which is non-positively connected to the permanent magnets (24) by means of a longitudinal press connection. [5] Brushless electric machine (10) according to claim 4, characterized bythat the at least one sleeve (64, 64', 64") has a seam (70) which runs substantially perpendicular to a longitudinal axis (A) of the machine shaft (16) of the brushless DC machine (10). [6] Brushless electric machine (10) according to one of the preceding claims 4 or 5, characterized by that the at least one sleeve (64, 64', 64") has at an open end (66) a diameter which is different from the inner diameter (D I ) of the sleeve (64, 64', 64") has an expanding insertion phase (68, 68', 68"), the inner diameter (D P ) is larger than an outer diameter (D R ) of the rotor (18) with the mounted permanent magnets (24). [7] Electric motor-driven machining device, in particular electric hand tool, with a brushless electric machine (10) according to claim 1. [8] Method for producing a brushless electric machine (10) according to one of the preceding claims 1 to 6, characterized bythat the reinforcement (56) is pushed onto the permanent magnets (24) of the rotor (18) in the direction of the longitudinal axis (A) of the machine shaft (16) and is non-positively connected to the permanent magnets (24) by means of a longitudinal press connection. [9] Method according to claim 8, characterized by that the reinforcement (56) during the longitudinal compression connection by expanding its inner diameter (D I ) is plastically irreversibly deformed.

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