Brushless motor and method for producing brushless motor
By using thin-walled reinforcements with high elastic modulus and high yield limit to fix the permanent magnet in brushless motors, the problem of insufficient fixation of permanent magnets at high speeds is solved, and a small magnetic gap and high efficiency motor operation is achieved.
Patent Information
- Application Number
- CN202410734287.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-06-07
- Filing Date
- 2024-06-07
- Publication Date
- 2024-12-10
AI Technical Summary
Existing brushless motors have insufficient fixation of permanent magnets at high speeds, resulting in greater impact on magnetic current, low efficiency, and low mechanical strength of surface magnets, which are prone to failure.
Thin-walled reinforcements are used to fix the permanent magnet on the rotor, with an elastic modulus of at least 150 GPa and/or a yield limit of 600 MPa. Through longitudinal extrusion connection and material locking, the permanent magnet is securely fixed at high speeds and kept small. Magnetic gap to improve motor efficiency.
Effectively fix the permanent magnet at high speeds above 20000rpm, maintain a small magnetic gap, improve the efficiency of the motor, avoid plastic deformation of the reinforcement, and enhance the mechanical strength and reliability of the motor.
Smart Images
Figure CN119109234A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a brushless motor, in particular a brushless DC motor, which comprises a stator and a rotor which is arranged in the stator so as to be rotatable relative to the stator, wherein the rotor comprises a cylindrical base body which is connected to the motor shaft in a rotationally fixed manner and carries a plurality of permanent magnets on its outer circumference, and the stator comprises a stator winding which comprises a plurality of single-tooth windings for driving the rotor by means of an electrically generated rotating magnetic field. Background Art
[0002] A brushless motor is to be understood in particular as a motor having a stator-side AC winding which is controllable or adjustable such that a rotating magnetic field is generated which attracts a permanently excited rotor. Alternatively, it is also conceivable to use the rotor in conjunction with a generator.
[0003] The rotor of a brushless motor, in particular a brushless direct current motor, BLDC (brushless direct current) motor or EC (electronically commutated) motor for short, with permanently excited magnets, is usually manufactured in two different structures. On the one hand, permanent magnets of different polarity can be embedded in so-called recesses of a cylindrical base body, and on the other hand, magnets or correspondingly alternatingly polarized magnetic rings can be applied to the base body from the outside as surface magnets. The base body usually consists of a plurality of rotor laminations stacked into a rotor lamination stack, which are respectively punched out of a soft magnetic sheet. However, other configurations of the rotor of an electric motor, in particular an EC motor, are also conceivable. For example, the cylindrical base body of the rotor can be composed of a composite material (soft magnetic composite material - SMC). SMC materials are made of high-purity iron powder with a special surface coating on each particle. This electrically insulating surface ensures high electrical resistance even after pressing and heat treatment, which in turn leads to a reduction or avoidance of eddy current losses. SMC materials are known to those skilled in the art, so their composition should not be discussed further here.
[0004] The permanent magnets of the magnetic ring are especially made of hard magnetic materials such as iron alloys, cobalt alloys or nickel alloys. If the permanent magnets are designed as surface magnets, they can be magnetized before or after being installed on the rotor. In addition, plastic-bonded permanent magnets are conceivable, whose magnetic powder is embedded in a matrix composed of a plastic binder. The magnetic powder can be made of hard ferrite, SmCo and / or NdFeB, or be constructed as an AlNiCo alloy. Preferably, the plastic binder is constructed as a thermoplastic binder, such as polyamide or polyphenylene sulfide. Alternatively, it is also conceivable that the plastic binder is constructed as a thermosetting binder, such as an epoxy resin.
[0005] Compared to embedded magnets, surface magnets have many advantages but also the disadvantage that they have a lower mechanical strength relative to the centrifugal forces acting on the surface magnets during motor operation. Therefore, in order to avoid defects and malfunctions, in addition to the mechanical strength of the surface magnets, their fixing to the base body is also of great significance.
[0006] DE 11 2016 0004 207 T5 discloses a rotor for an electric machine, which comprises a rotor core, a plurality of permanent magnets, an electrically conductive element and a retaining element. The permanent magnets are arranged at the peripheral region of the rotor core and are spaced apart from each other via pole gaps in the circumferential direction. The electrical conductivity of the electrically conductive element is higher than the electrical conductivity of the permanent magnets. The electrically conductive element surrounds the rotor core and the plurality of permanent magnets as a whole and has first and second regions facing each other, which face each other in the circumferential direction via a gap. Finally, the retaining element surrounds the rotor core, the plurality of permanent magnets and the electrically conductive element as a whole. Summary of the invention
[0007] The object of the present invention is to provide a brushless electric machine whose permanent magnets arranged on the outer circumference of the rotor are held by means of reinforcement elements which are improved compared to the prior art and which influence the magnetic flux between the stator and the rotor as little as possible.
[0008] In order to solve the proposed task, it is provided that the permanent magnets of the rotor are fixed by means of thin-walled reinforcements surrounding them in the radial direction, wherein the reinforcements have an elastic modulus of at least 150 GPa (gigapascal) and / or a yield limit of at least 600 MPa (megapascal). It is particularly advantageous that on the one hand the permanent magnets can be firmly fixed even at very high rotation speeds of more than 20,000 rpm (revolutions per minute) of the brushless motor, and on the other hand the magnetic gap between the rotor and the stator can be kept as small as possible to increase the efficiency of the motor. Despite the small wall thickness of the reinforcement, the high elastic modulus results in very small deformations. The advantage of the high yield limit is that plastic deformations on the outer circumference of the reinforcement can be avoided even during short-term tests at twice the maximum rotation speed of the rotor.
[0009] In addition, the present invention relates to an electrically driven processing tool, in particular a handheld electric machine tool, having a brushless motor according to the present invention. In the context of the present invention, a machine tool that is battery-operated and / or power-mains-operated and is used to process a workpiece by means of an insertion tool driven by a brushless motor should also be understood as an electrically driven processing tool. Here, the electric processing tool can be configured as a handheld machine tool or as a fixed machine tool. In this case, typical machine tools are hand drills or vertical drills, screwdrivers, impact drills, planers, angle grinders, vibration grinders, polishers, etc. However, correspondingly driven garden tools and construction tools such as mowers, lawn mowers, branch saws, electric milling and groove milling, blowers, robot crushers, and robot excavators can also be considered as electric tools. In addition, the present invention can be applied to brushless motors of household appliances such as vacuum cleaners, mixers, etc.
[0010] In another configuration, the reinforcement is made of a paramagnetic metal, in particular aluminum, brass, stainless steel, etc. Alternatively, the reinforcement can also be made of a plastic with a maximum magnetic permeability of 15, in particular a maximum magnetic permeability of 2, or a composite material formed by plastic and paramagnetic metal. Paramagnetic metals are metals with a magnetic permeability greater than 1, which are not strongly attracted by magnets and cannot be magnetized by themselves. Therefore, paramagnetic metals are significantly different from ferromagnetic metals such as iron and diamagnetic metals such as copper in their magnetic properties. It should be pointed out at this point that the concept of non-magnetic is sometimes used for paramagnetic or non-ferromagnetic materials. However, strictly speaking, there is no non-magnetic material, because every material will react magnetically from a certain intensity of the magnetic field to which it is exposed. Particularly advantageously, reinforcements made of paramagnetic metals and / or plastics with low magnetic permeability prevent partial or complete short circuits of the magnetic circuit of the brushless motor.
[0011] The reinforcement element is designed as at least one hollow cylindrical sleeve which is connected to the permanent magnet in a force-locking manner by means of a longitudinal press connection. This makes the brushless motor particularly easy to manufacture, since the at least one sleeve can be pushed onto the permanent magnet of the rotor along the longitudinal axis of the motor shaft for the longitudinal press connection. In this case, the at least one sleeve is irreversibly plastically deformed during the longitudinal press connection by expanding its inner diameter.
[0012] At least one sleeve may be provided with a slit which extends substantially perpendicularly to the longitudinal axis of the motor shaft of the brushless DC motor. Unlike seamless sleeves, the slit makes the manufacturing process of the sleeve simpler. The reinforcement may also consist of a plurality of sleeves which are pushed onto the permanent magnets. In this case, the individual sleeves of the reinforcement may be pushed onto the permanent magnets mounted on the rotor successively from one direction or, in particular in the case of an even number of sleeves, in pairs from two directions along the longitudinal axis of the motor shaft.
[0013] The at least one sleeve can be pushed on in a particularly advantageous and simplified manner by virtue of the sleeve having an introduction groove at the open end which is widened relative to its inner diameter and whose inner diameter is larger than the outer diameter of the rotor with the installed permanent magnets. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Refer to the following Figures 1 to 11 The present invention is explained by way of example, wherein the same reference numerals in the figures represent the same parts having the same functions. The accompanying drawings show:
[0015] Figure 1 : A cross-sectional view of a three-phase brushless motor according to the prior art,
[0016] Figure 2 :Used to control the Figure 1 The block diagram of the circuit of the motor constructed as a brushless DC motor,
[0017] Figure 3 : A cross-sectional view of a first embodiment of a brushless motor according to the present invention,
[0018] Figure 4 : A perspective view of a second embodiment of a rotor of a brushless motor according to the present invention,
[0019] Figure 5 According to the present invention, the fixing Figure 4 The cross section of the sleeve of the permanent magnet of the rotor,
[0020] Figure 6 : A perspective view of a third embodiment of a rotor of a brushless motor according to the present invention,
[0021] Figure 7 : A perspective view of a first embodiment for connecting a sleeve according to the invention to a permanent magnet,
[0022] Figure 8 :according to Figure 7 A top view of an embodiment of a single welding point,
[0023] Fig. 9 : A perspective view of a second embodiment for connecting a sleeve according to the invention with a permanent magnet,
[0024] Fig.10 : A perspective view of a third embodiment for connecting a sleeve according to the present invention to a permanent magnet and
[0025] Fig.11 : A perspective view of a fourth embodiment for connecting a sleeve according to the present invention to a permanent magnet. DETAILED DESCRIPTION
[0026] Figure 1A cross section of a brushless motor 10 according to the prior art is shown, which is designed as a three-phase brushless direct current motor (BLDC motor or EC motor) 12, which has a stator 14 and a rotor 18 arranged in a rotationally fixed manner on a motor shaft 16. The brushless direct current motor 12 is used to drive a processing tool, not shown in detail, such as a vacuum cleaner, a machine tool, etc. Instead of the BLDC motor or EC motor 12, an alternating current motor (AC motor), such as an asynchronous motor or a synchronous motor, can also be considered. The rotor 18 of the brushless direct current motor 12 includes a cylindrical base body 20, which has a plurality of permanent magnets 24 designed as surface magnets on its outer circumference 22, and the polarities N and S of these permanent magnets are alternated in the circumferential direction of the rotor 18. In this embodiment, four permanent magnets 24 are shown, which themselves 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, wherein each two opposing single-tooth windings 28 form a winding strand 30 of a three-phase stator winding 32. The stator 14 defines a cylindrical cavity by its stator teeth 26, in which the rotor 18 is arranged and can rotate relative to the stator 14 by means of the motor shaft 16. When current is passed through the winding strands 30, a rotating magnetic field is generated, which causes the permanently excited rotor 18 and the motor shaft 16 to rotate. It should be pointed out as a precaution that the following invention is not only applicable to brushless motors 10 designed as electric motors. The brushless motor 10 can also be designed as a correspondingly constructed generator. However, the invention is described below only with reference to the brushless DC motor 12.
[0027] Figure 2 Displays the control Figure 1 The device 34 for the brushless DC motor 12. In addition to the brushless DC motor 12, the device 34 also includes a control or regulating unit 36, a drive circuit 38 and a comparator 40. For the sake of clarity, only the most important manufactured parts and components of the device 34 are shown. The control or regulating unit 36 can be constructed as a microprocessor (μP), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), etc. It is also conceivable that the control or regulating unit 36 is at least partially made of discrete semiconductor devices. The drive circuit 38 is constructed as an inverter in the form of a B6 bridge circuit and has a half-bridge 42 constructed as an inverter circuit for each phase strand or winding strand 30 of the three phases U, V, W of the stator winding 32. Each half-bridge 42 is connected to a high supply potential V H The first power switch 44 connected to the (high side) and the low power supply potential V LThe control or regulation unit 36 controls the individual power switches 44, 46 so that each of the two winding strands 30 is connected to the first winding strand 30 by means of a pulse width modulation signal or a plurality of pulse width modulation signals S PWM (the two should be used as synonyms here) in such a way that the first power switch 44 of one of the three half-bridges 42 is closed (for example, T1), while the first power switches 44 of the other two half-bridges 42 are opened (for example, T3 and T5), and the second power switch 46 of at least one of the other two half-bridges 42 is closed (for example, T2), while the second power switch 46 of at least the half-bridge 42 whose first power switch 44 (for example, T1) is closed is opened (for example, T4). In this way, the first power switch 44 and the second power switch 46 can be switched alternately to generate a rotating magnetic field, so that four of the six single-tooth windings 28 of the winding strands 30 are energized, so that the stator flux potential generated during operation is oriented perpendicularly to the rotor flux potential in the middle. In addition, in order to avoid short circuits, it is ensured that the two power switches 44 and 46 of the same half-bridge 42 are never closed at the same time (for example, T1 and T4). To this end, the power switches 44 and 46 of the same half-bridge 42 are always switched after the corresponding other power switch 44, 46 is opened by means of a pulse width modulation signal S PWM Closed with a certain delay time. Those skilled in the art are aware of this type of circuit, so it will not be discussed further. Instead of multiple B6 half-bridges, H bridges or similar inverter circuits can also be used to control the individual phases U, V, W of the brushless DC motor 12.
[0028] In order to be able to determine the exact switching time of the individual power switches 44, 46 of the drive circuit 38, the control or regulating unit 36 must know the position of the rotor 18. The determination of the rotor position can be carried out, for example, with the aid of a sensor (e.g., a Hall sensor) which is arranged on the stator 14 above the circumference of the rotor 18. However, instead of determining the rotor position based on a sensor, it is usually advantageous to determine the rotor position sensorlessly by means of back electromotive force in combination with electronic commutation, since this usually leads to lower costs due to the omission of sensors and to greater reliability in combination with a more compact design of the brushless motor 10. When utilizing the back electromotive force, the variation of the voltage induced by the permanent magnet 24 of the rotor 18 in the non-energized winding strand 30 is detected. To this end, according to the prior art, the strand current I of one of the phases U, V, W is first predicted. U ,I V ,I W The zero crossing of the pulse width modulation signal S PWMThe current supply to the corresponding winding strand 30 is interrupted for a predetermined time period, during which the predicted zero crossing occurs. U , U V , U W After that, the corresponding strand current I U ,I V ,I W Flows through a freewheeling element (not shown) connected in parallel with the switched-off power switches 44, 46. In the case of a MOSFET, the freewheeling element is realized, for example, by its own freewheeling diode. Since the freewheeling diode conducts in only one direction, once the strand current I U ,I V ,I W When the voltage reaches zero, a jump-like increase in voltage occurs. U , U V , U W Then determine the strand current I U ,I V ,I W The zero crossing of the strand current I U ,I V and I W The phase shift between the voltage and the back electromotive force is used to detect the position of the rotor 18.
[0029] exist Figure 2 In the exemplary embodiment shown, only phase U is used to detect the rotor position. For this purpose, the comparator 40 determines the potential V of the common star point 48 of the winding strands 30 of the brushless DC motor 12 which is present at the first input. SP and the potential V of the node 50 applied at the second input for energizing the corresponding winding strand 30 of the phase U BF,U The arithmetic difference between Diff In order to determine the potential V of the voltage induced in the non-current-carrying winding strand 30 BF,U , using a voltage divider 54 formed by at least two resistors 52, one end of which is connected to the node 50 and the other end is at a reference potential V GND , low supply potential V L Or a comparable reference potential. Arithmetic difference U Diff Then as the digitized back EMF signal S BF、U The signal is transmitted from the comparator 40 to the control or regulating unit 36 .
[0030] Figure 3 The invention is illustrated by means of a section through a brushless DC motor 12 perpendicular to the longitudinal axis A of the motor shaft 16. Figure 1The base 20 of the rotor 18, which is connected to the motor shaft 16 in a rotationally fixed manner, carries permanent magnets 24 with alternating polarities N and S on its outer circumference 22. The permanent magnets 24 are connected to the base 20 in a material-locked, form-locked and / or force-locked manner on the one hand, and are fixed by means of thin-walled reinforcements 56 surrounding them in the radial direction on the other hand. In order to make the permanent magnets 24 firmly fixed even at very high speeds of more than 20,000 rpm of the brushless DC motor 12 and the magnetic gap between the rotor 18 and the stator 14 can be kept as small as possible to maintain or improve efficiency, the reinforcement 56 has an elastic modulus of at least 150 GPa and / or a yield strength of at least 600 MPa. In this case, although the wall thickness is small, very small deformations can be caused by the high elastic modulus, and undesirable plastic deformations on the outer circumference 58 of the reinforcement 56 can be avoided by the high yield strength.
[0031] In order to prevent the magnetic circuit of the brushless motor 12 from being partially or completely short-circuited, the reinforcement 56 is made of a paramagnetic metal, in particular aluminum, brass, stainless steel, etc. Alternatively, the reinforcement 56 may also be made of a magnetic permeability μ r The invention is made of a plastic with a maximum of 15, in particular a maximum of 2, or a composite material composed of plastic and paramagnetic metal.
[0032] A pole gap 60 is provided between two adjacent permanent magnets 24 mounted on the base body 20 of the rotor 18. In order to fix the permanent magnets 24 in a form-fitting or force-fitting manner, the base body 20 of the rotor 18 has protrusions 62 distributed on its outer circumference 22, by means of which the permanent magnets 24, which are preferably not yet magnetized, can be positioned with a defined pole gap 60. These protrusions 62 can be configured, for example, as bumps, strips, etc. on the base body 20. Alternatively or in addition, the permanent magnets 24 can also be connected to the base body 20 in a material-locking manner (for example, by means of bonding). The pole gap 60 allows optimization in terms of the power density of the brushless DC motor 12 and in terms of the full utilization of the magnetic material used for the permanent magnets 24. Therefore, a compromise between the cost and efficiency of the brushless DC motor 12 can be easily achieved as required, in that the pole gap 60 is kept as small as possible on the one hand, so as not to reduce or only reduce the power density of the brushless DC motor 12 to a minimum, and on the other hand is designed so large that the magnetic material used is fully utilized as much as possible. To this end, the width W of the pole gap 60 in the circumferential direction is equal to the outer diameter D of the rotor 18 on which the permanent magnets 24 are provided. R (See Figure 4 ) is preferably less than 10%. The thin-walled reinforcement 56 is preferably understood herein as a reinforcement 56 having a thickness T less than its inner diameter D I 2%.
[0033] In order to manufacture the brushless DC motor 12 according to the present invention, in a first method step, a plurality of initially unmagnetized or weakly magnetized permanent magnets 24 are mounted on the outer periphery 22 of the base 20 of the rotor 18, in particular by means of an assembly device not shown in detail, so that a pole gap 60 is retained between two adjacent permanent magnets 24. Here, the permanent magnets 24 can be fixed to the base in a material-locked, shape-locked and / or force-locked manner in the above-mentioned manner. In a subsequent method step, the reinforcement member 56 is pushed onto the permanent magnet 24 of the rotor 18 in the direction of the longitudinal axis A of the motor shaft 16. This can also be preferably accomplished automatically by an assembly device. During the pushing process, the reinforcement member 56 is connected to the permanent magnet 24 by a force-locked longitudinal extrusion connection, so that the reinforcement member 56 passes through its inner diameter D I expansion and irreversible plastic deformation (see Figure 5 Before the rotor 18 is inserted into the stator 14 , in a further method step, the permanent magnets 24 are magnetized by means of at least one magnetizing coil of an assembly device.
[0034] Due to the pole gap 60 between two respectively adjacent permanent magnets 24, the advantage is obtained that the initially unmagnetized or weakly magnetized permanent magnets 24 are simply, subsequently and mainly completely magnetized. Complete magnetization leads to significantly higher magnetic fluxes, so that the permanent magnets 24 also make a significant contribution to the torque generation of the brushless DC motor 12 in their edge regions. In addition, the unmagnetized or weakly magnetized permanent magnets 24 can be positioned more easily and more accurately on the outer circumference 22 of the base body 20 of the rotor 18, because they do not emit or at least only emit a small magnetic attraction force.
[0035] Figure 4 A perspective view of another embodiment of a rotor 18 is shown. The reinforcement element 56 is designed as a hollow cylindrical sleeve 64, which is connected to the permanent magnets 24 of the rotor 18 in a force-fitting manner by means of a longitudinal press connection. During the longitudinal press connection, the sleeve 64 is formed by its inner diameter D I The expansion of the Figure 3 The reinforcement element 56 can also be designed, for example, as a ring extending only over a portion of the length of the base body 20 of the rotor 18, while the sleeve 64 completely surrounds the permanent magnets 24. The sleeve 64 thus extends over the entire length of the base body 20 of the rotor 18 in the direction of the longitudinal axis A of the motor shaft 16. At one open end 66, the sleeve 64 has a diameter D I The expanded lead-in groove 68 has an inner diameter D P is larger than the outer diameter D of the rotor 18 on which the permanent magnets 24 are mounted. R This makes it possible to easily push the sleeve 64 along the longitudinal axis A of the motor shaft 16 .
[0036] To illustrate, in Figure 51 shows a thin-walled sleeve 64 of thickness T which has not yet been pushed onto the rotor 18 in a section along the longitudinal axis A. It can be seen that the inner diameter D of the introduction groove 68 at the open end 66 of the sleeve 64 is P Greater than the inner diameter D of the hollow cylindrical portion thereof I In order to achieve a longitudinal press connection during the installation of the sleeve 64, the inner diameter D of the hollow cylindrical part of the sleeve 64 in the uninstalled state is I must be smaller than the outer diameter D of the base body 20 of the rotor 18 on which the permanent magnets 24 are provided. R Therefore, when the sleeve 64 is not installed, the relationship D is applicable. P >D R >D I Furthermore, due to the correspondingly high yield strength of the sleeve 64 of at least 600 MPa, undesired plastic deformations of the sleeve 64 at its outer circumference 58 during operation of the brushless DC motor 12 can be avoided. This makes it possible, on the one hand, to achieve very small magnetic gaps between the rotor 18 and the stator 14 without the risk of mechanical contact and, on the other hand, to ensure the concentricity of the rotor 18 even at very high rotational speeds.
[0037] Figure 6 Another embodiment of the invention is shown, in which the reinforcement element 56 is formed by two sleeves 64', 64", which are joined together by means of a slot 70 extending substantially perpendicularly to the longitudinal axis A of the motor shaft 16. Figure 4 and Figure 5 Unlike the seamless sleeve 64, the seam 70 allows the sleeves 64', 64" to be manufactured and assembled more simply, especially when the extension dimension of the base body 20 of the rotor 18 is particularly long. Here, the sleeves 64', 64" can be connected by material locking by means of the seam 70 before being pushed onto the permanent magnet 24, especially welded, so that after the connection they have an introduction groove 68', 68" at their open ends 66', 66", respectively. Alternatively, it is also conceivable that the individual sleeves 64', 64" of the reinforcement member 56 are pushed onto the permanent magnet 24 mounted on the base body 20 of the rotor 18 in pairs from one direction or from two directions along the longitudinal axis A of the motor shaft 16, especially in the case of an even number of sleeves 64, and then connected by material locking by means of the seam 70. If the sleeves 64', 64" are made of plastic or a composite material, the seam 70 connecting them can also be produced by means of laser welding or the like. Adhesion of the seam 70 is also conceivable.
[0038] Figure 7A first embodiment for connecting a reinforcement member 56 configured as a sleeve 64 to a permanent magnet 24 is shown in a perspective view. For illustration, the base body 20 of the rotor 18 and the motor shaft 16 are omitted. However, it should be noted that the permanent magnet 24 has been installed on the base body 20 of the rotor 18 before the sleeve 64 is pushed on as described above, observing the pole gap 60 arranged between them. The sleeve 64, which is especially made of paramagnetic metal, is connected to the permanent magnet 24 by a plurality of welding points 72 in a material-locked and / or form-locked manner. The welding points 72 can be automatically set in a particularly advantageous manner by means of a corresponding welding device, particularly a laser, of an assembly device, which is not shown in detail, after the sleeve 64 is pushed on the permanent magnet 24. It is also conceivable to manually set the welding points 72. In this way, brushless DC motor 12, in particular rotor 18 thereof, can be effectively and cost-effectively protected even at very high rotational speeds of more than 20,000 rpm and in the event of impacts, falls, etc., from damage, for example due to deformation of sleeve 64 and / or axial sliding along longitudinal axis A of motor shaft 16.
[0039] The number, shape and distribution of the welding points can vary depending on the operating parameters of the brushless DC motor 12 and / or the sleeve 64. For example, the number of welding points 72 should be as large as possible or at least as much as necessary to securely fix the sleeve 64, but as small as possible or at most as much as necessary to avoid affecting the magnetic flux between the rotor 18 and the stator 14. Figure 7 , three welding points 72 are respectively arranged along the longitudinal axis A in the region of the pole gap 60, two of which are near the open end 66 and the third is substantially at half the length of the sleeve 64. In the case of a longer or shorter sleeve 64, more or fewer welding points 72 can be arranged accordingly. In addition, depending on the outer diameter D of the rotor 18 R Depending on the number of permanent magnets 24 or pole gaps 60, it is also possible that welding points 72 are not provided near each pole gap 60, but rather that individual pole gaps 60 are left blank. However, it is advantageous if the number of welding points 72 per permanent magnet 24 is in the range from 1 to 10, in particular in the range from 2 to 4, wherein, as mentioned above, this depends largely on the size of the rotor 18 and the number, size and shape of the permanent magnets 24.
[0040] Figure 8In the top view, a single weld point 72 is shown. In addition to a material-locking connection, a form-locking connection can also be produced by means of a laser, so that the focal point is heated intensively for a short time, so that a melt column is formed, which softens or liquefies parts of the sleeve 64 and the permanent magnet 24. After the melt column solidifies, undercuts and / or protrusions are produced between the sleeve 64 and the permanent magnet 24, which lead to a form-locking connection. In addition to optimizing the number of weld points 72, alternatively or additionally, their size or shape can also be varied in such a way that they each have a diameter D of approximately 0.2 to 2 mm. S . For a material-locked connection, both the sleeve 64 and the permanent magnet 24 must be made of a corresponding weldable material. For the sleeve 64, this is ensured in particular by paramagnetic metals, but there are also plastics and composite materials that are suitable for welding to the permanent magnet 24. The material of the permanent magnet 24 should preferably be sintered or hot-pressed. Of course, plastic-composite permanent magnets 24 can also be used here. The corresponding situation also applies to possible coatings and surface layers of the sleeve 64 and the permanent magnet 24. Through the number, shape and distribution of the welding points 72, possible imbalances of the rotor 18 can also be compensated to a certain extent, so that the welding points 72 do not have to be arranged symmetrically distributed on the outer circumference 58 of the sleeve 64.
[0041] Fig. 9 A second exemplary embodiment for the material-locking and / or form-locking connection of the sleeve 64 and the permanent magnet 24 by means of a plurality of weld points 72 is shown in a perspective view. Figure 8 Differently, two welding points 72 are arranged on each permanent magnet 24 substantially centrally in the circumferential direction of the sleeve 64 along the longitudinal axis A. Here, the welding points 72 are located near the two open ends 66 of the sleeve 64. However, it is also conceivable that more welding points can be arranged along the longitudinal axis A depending on the length of the sleeve 64. It is also conceivable that the outer diameter D of the rotor 18 R In smaller cases, not every permanent magnet 24 is connected to the sleeve 64 in a form-fitting and / or force-fitting manner via a weld point 72 .
[0042] Fig.10 A third embodiment is shown for connecting sleeve 64 and permanent magnet 24 by means of a plurality of weld points 72. Here, each permanent magnet 24 is provided with four weld points 72, so that the weld points are close to pole gap 60 in the edge region of permanent magnet 24 near both open ends 66 of sleeve 64.
[0043] Fig.11A fourth embodiment for connecting the sleeve 64 and the permanent magnet 24 is shown. In this case, after the sleeve 64 has been pushed on, a ring 74 is arranged on an open end 66 of the sleeve 64, in particular on the open end 66 opposite the open end 66 with the introduction groove 68, in such a way that the ring is connected to the permanent magnet 24 on the end face side and to the sleeve 64 at its circumferential edge 76 by a plurality of welding points 72. Here, the permanent magnet 24 can be provided with one welding point 72. However, depending on the outer diameter D of the rotor 18, the outer diameter D of the rotor 18 can be increased. R Depending on the number of permanent magnets 24, more or fewer welding points 72 are conceivable. Preferably, the ring 74 is made of the same material as the sleeve 64. In addition, a ring 74 can be provided at each open end 66 of the sleeve 64. Instead of a ring 74, the sleeve 64 can also have individual tongues at at least one of its open ends 66, which are bent after being pushed onto the permanent magnets 24 and welded to the permanent magnets 24 on the end side.
[0044] Finally, it should be pointed out that the present invention is not limited to Figures 3 to 11 The exemplary embodiments shown are not intended to be understood as examples. 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 restrictive. This also applies to the brushless DC motor 12 and the electronics for controlling it, which must be adapted accordingly when the brushless motor 10 is designed as a generator.
Claims
1. A brushless electric motor (10), in particular a brushless direct current motor (12), comprising a stator (14) and a rotor (18) arranged in the stator so as to be rotatable relative to the stator, wherein: The rotor (18) has a cylindrical base body (20) which is connected to the motor shaft (16) in a rotationally fixed manner and carries a plurality of permanent magnets (24) on the outer circumference (22) of the base body, and 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 in that the permanent magnets (24) of the rotor (18) are fixed by means of thin-walled reinforcements (56) surrounding them in the radial direction, wherein the reinforcements (56) have an elastic modulus of at least 150 GPa and / or a yield strength of at least 600 MPa.
2. The brushless motor (10) according to claim 1, characterized in that: The reinforcement (56) is made of paramagnetic metal, in particular aluminum, brass, stainless steel or similar material.
3. The brushless motor (10) according to claim 1, characterized in that: The reinforcing element (56) is made of a material having a magnetic permeability (μ) of at most 15, in particular at most 2. r ) plastic, or a composite material formed by plastic and paramagnetic metal, especially aluminum, brass, stainless steel, etc.
4. The brushless motor (10) according to one of the preceding claims, characterized in that The reinforcement element (56) is designed as at least one hollow cylindrical sleeve (64, 64', 64") which is connected to the permanent magnet (24) in a non-positive manner by means of a longitudinal press connection.
5. The brushless motor (10) according to claim 4, characterized in that: The at least one sleeve (64, 64', 64") has a slot (70) extending substantially perpendicularly to a longitudinal axis (A) of a motor shaft (16) of the brushless DC motor (10).
6. The brushless motor (10) according to claim 4 or 5, characterized in that: The at least one sleeve (64, 64', 64") has, at the open end (66), an inner diameter (D) of the sleeve (64, 64', 64") I ) an expanded introduction groove (68, 68', 68"), the inner diameter of the introduction groove (D P ) is larger than the outer diameter (D R ).
7. An electrically powered machining tool, in particular an electric handheld machine tool, having a brushless electric motor (10) according to claim 1.
8. Method for producing a brushless motor (10) according to any one of claims 1 to 6, characterized in that The reinforcement element (56) is pushed onto the permanent magnet (24) of the rotor (18) in the direction of the longitudinal axis (A) of the motor shaft (16) and connected to the permanent magnet (24) in a non-positive manner by means of a longitudinal press connection.
9. The method according to claim 8, characterized in that The reinforcement (56) is formed during the longitudinal extrusion connection by its inner diameter (D I ) expansion and irreversible plastic deformation.