Electric motor with a rotor having a burst protection sleeve but not bonded to the magnet element

Abstract

The present invention relates to an electric motor (1) comprising a stator (2) and a rotor (4) rotatably mounted relative to the stator (2) about a rotation axis (3). The rotor (4) further has: a main part (5); a plurality of magnet elements (7) which are distributed along the circumferential direction and are received in a spaced-apart manner on a radial surface (6) of the main part (5); and a burst protection sleeve (8) which covers the main part (5) and the magnet elements (7). The burst protection sleeve (8) has: a plurality of covering sections (9), each of the plurality of covering sections directly contacting the magnet elements (7); and a plurality of bridging regions (10) which connect two adjacent covering sections (9) together, wherein the burst protection sleeve (8) is used to directly support the magnet elements (7) relative to the main part (5), and the bridging regions (10) have a lower bending strength in the circumferential direction than the covering sections (9).

Description

Technical Field

[0001] The present invention relates to an electric motor, which is preferably used in an actuator of an actuating device of a motor vehicle. The electric motor has a stator and a rotor rotatably mounted relative to the stator about a rotation axis. The rotor further has: a main part; a plurality of magnet elements distributed along a circumferential direction and received in a radially facing surface of the main part at intervals from each other; and a burst protection sleeve covering the main part and the magnet elements, and the burst protection sleeve has: a plurality of covering sections, each of the plurality of covering sections directly contacting the magnet elements; and a plurality of bridging areas connecting two adjacent covering sections together. Background Art

[0002] Conventional electric motors are well known in the prior art. For example, DE 10 2018108 595A1 discloses a motor having a burst protection sleeve with magnetic sections and less magnetic sections. Therefore, it is known to equip the rotor of an electric motor with a burst protection sleeve, which ensures that component loosening during the operation of the electric motor does not immediately damage other components of the electric motor.

[0003] However, a disadvantage of these designs known from the prior art is that the manufacturing effort of the burst protection sleeve is relatively high. This is because adhesive connections are usually used to firmly fix the magnet elements to the main part of the rotor. However, the manufacturing cost of these adhesively bonded rotors is relatively high. In addition, the magnetic resistance in the magnetic circuit between the stator and the rotor resulting therefrom is relatively high due to the arrangement of these adhesive connections. Summary of the Invention

[0004] Therefore, the object of the present invention is to eliminate the disadvantages known from the prior art and, in particular, to provide an electric motor that can be manufactured and assembled with less effort and provides as high an efficiency as possible.

[0005] According to the present invention, this is achieved by using a burst protection sleeve to directly support the magnet elements relative to the main part, wherein the bending strength of the bridging area in the circumferential direction is lower than that of the covering section.

[0006] Compared with the covering section, a region with lower rigidity is intentionally introduced into the burst protection sleeve via the bridging area, so that the entire burst protection sleeve can expand to a certain extent. This makes the assembly of the burst protection sleeve easier and makes the assembly possible in the case of a high overlap occurring during the press fit into the rotor magnet. Compared with the designs according to the prior art, the assembly effort is significantly reduced by eliminating the need for the previously used adhesive bonding.

[0007] Other embodiments according to the invention are claimed by the dependent claims and are explained in more detail below.

[0008] It is thus more advantageous if the burst protection sleeve is fixed to the magnet element attached to the main part / fixed to the pre-assembly formed by the main part and the magnet element via a press fit. This ensures that the burst protection sleeve is fastened as firmly as possible.

[0009] If the corresponding bridging area has a recess in the shape of a groove, the bridging area has a shape that is as easy to manufacture as possible. The recess in the shape of a groove is preferably formed by bending or deep drawing.

[0010] If the corresponding bridging area is open towards one axial end of the burst protection sleeve or towards both axial ends, the corresponding bridging area exhibits a bending strength that is as constant as possible along the length of the bridging area, which further reduces the assembly effort.

[0011] If the burst protection sleeve has a diameter change, preferably an increase in diameter, at one axial end, an assembly aid for the burst protection sleeve is provided in a simple manner. This is because such a diameter change allows the burst protection sleeve to slide onto or into the pre-assembly including the main part and the magnet element and is guided during the initial stage of the assembly process.

[0012] In this context, it is also useful if, at the axial end of the burst protection sleeve, each covering section has an extension that projects axially obliquely, thereby forming a diameter change.

[0013] In this regard, it is also useful if each bridging area is provided with a rising side near the axial end of the burst protection sleeve, thereby forming a diameter change.

[0014] In other words, the diameter change is thus preferably formed by a tapered widening or a tapered annular edge. This results in the following insertion aid: the insertion aid is as easy to manufacture as possible for inserting the assembly including the main part and the magnet element into the burst protection sleeve. The annular edge is preferably formed directly during the formation of the burst protection sleeve, preferably by stamping or deep drawing directly.

[0015] The rotor is further arranged relative to the stator such that the extension is arranged axially adjacent to the magnet element. Thus, the performance of the electric motor is not adversely affected by the presence of the annular edge.

[0016] Furthermore, it has proven advantageous if the electric motor is designed as a brushless DC motor.

[0017] In other words, the present invention provides an improved version of a BLDC rotor having a surface magnet (magnet element) and a burst protection sleeve, which does not require any adhesive bonding with the magnet in terms of manufacturability and mountability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

[0019] In the drawings:

[0020] Figure 1 A longitudinal sectional view of an electric motor according to a preferred exemplary embodiment of the present invention is shown, in which the overall structure of the electric motor can be clearly seen.

[0021] Figure 2 Shows Figure 1 A detailed view of the area marked "II" located at the axial end of the burst protection sleeve of the rotor in.

[0022] Figure 3 Shows according to Figure 1 A perspective view of the electric motor of.

[0023] Figure 4 Shows as viewed from the front side Figures 1 to 3 A perspective view of the burst protection sleeve used in.

[0024] Figure 5 Shows for illustrating the extended annular edge of the burst protection sleeve Figure 4 A detailed view of the area marked "V" in.

[0025] Figure 6 A perspective view of the burst protection sleeve as viewed from the rear side is shown.

[0026] Figure 7 Two side views of the burst protection sleeve are shown, in which the left partial view shows the entire burst protection sleeve and the right partial view shows the angled protruding extension of the annular edge.

[0027] Figure 8 A cross-sectional view of a rotor having a burst protection sleeve is shown.

[0028] Figure 9 Shows in Figure 8 A detailed view of the area marked "IX" in.

[0029] Figure 10 Shows Figure 9 A perspective view of the detailed area shown in.

[0030] Figure 11A perspective view of the rotor shown in a longitudinal section is shown.

[0031] Figure 12 A perspective view of a partially disassembled electric motor is shown, in which the rotor and the stator are shown separated from each other; and

[0032] Figure 13 A disassembled view of the rotor is shown. DETAILED DESCRIPTION

[0033] These drawings are merely schematic in nature and are only for understanding the present invention. The same elements are provided with the same reference numerals.

[0034] Using Figure 1 、 Figure 3 and Figure 12 The basic structure of the electric motor 1 according to the present invention can be easily recognized. The electric motor 1 is equipped with a stator 2 having an integral annular design. In this embodiment, the stator 2 has a plurality of stator laminations 17 arranged in a stack along the axial direction, that is, along the rotation axis 3 of the rotor 4 of the electric motor 1. The stator laminations 17 are received on a stator housing / stator carrier 18. A winding 19 is also typically provided, and the winding can be seen in the cross-sectional view in Figure 1 to be located on the stator laminations 17 near the axial end face of the stack 20.

[0035] Furthermore, the rotatably mounted rotor 4 is radially arranged inside the stator 2 (with respect to the rotation axis 3). In this embodiment, the rotor 4 is thus realized as an inner rotor. However, in other embodiments, the rotor can in principle also be realized as an outer rotor.

[0036] In this embodiment, the rotor 4 has a one-piece main part 5. This main part 5 is also referred to as a rotor carrier. The main part 5 is preferably realized as a sintered component. In other embodiments according to the present invention, the main part 5 is alternatively provided in a plurality of parts with a number of rotor laminations (each rotor lamination is preferably made of an electrical sheet), and the number of rotor laminations are arranged in a stack to form a lamination stack.

[0037] Here, a number of magnet elements 7 in the form of permanent magnets are arranged uniformly distributed in the circumferential direction on the main part 5. The circumferential direction is understood as the direction along an imaginary circular line extending coaxially with the rotation axis 3. The magnet elements 7 are located on a radial side portion 6, and the radial side portion is in this case the radially outer side portion of the main part 5. In this context, reference can also be made to Figures 8 to 13 These drawings show the structure of the rotor 4 in more detail. When observed in a cross-section, the magnet elements 7 formed as circular arc segments directly support on the radially outer surface 21 (housing surface) of the main part 5.

[0038] According to the present invention, the burst protection sleeve 8 is pressed onto / fixed to a pre-assembled part including a main part 5 and a magnet element 7 via a press fit 16. The burst protection sleeve 8 is radially pressed onto the magnet element 7 from the outside while supporting the magnet element 7 on the main part 5.

[0039] The burst protection sleeve 8 is designed to be continuous in the circumferential direction, i.e., is designed to be completely annular. According to Figures 4 to 7 , the burst protection sleeve 8 is provided with a number of regions of different hardness. For this purpose, the burst protection sleeve 8 has a plurality of plate-shaped covering sections 9, which are arranged in a distributed manner in the circumferential direction and extend in the shape of circular arc sections (following the outer surface of the magnet element 7). Thus, each covering section 9 lies flat on the magnet element 7 from the radially outer side. Two covering sections 9 that are arranged adjacent to each other in the circumferential direction are connected by a bridging region 10. Compared with the covering section 9, the bridging region 10 is intentionally reduced / lowered in terms of its bending strength in the circumferential direction by the design of its geometry.

[0040] Upon closer observation, each bridging region 10 shows a groove-shaped recess 11. The recess 11 extends in the axial direction of the burst protection sleeve 8. In the exemplary embodiment shown, the recess 11 extends continuously along the entire (axial) length of the burst protection sleeve 8. For example, in Figure 6 it can be clearly seen that the recess 11 is completely open towards the first axial end 12a of the burst protection sleeve 8; the recess 11 is also open towards the second axial end 12b opposite to the first axial end 12a. However, compared with the first end 12a, the recess 11 is only locally open due to the diameter change described in more detail below. This results in the geometry of the burst protection sleeve 8 being able to expand or contract.

[0041] Each bridging region 10 forms a radial clearance / distance 22 from the radial projection 23 of the main part 5 ( Figure 9 ). The projection 23 of the main part 5 is used to pre-position the magnet element 7. The recess 11 thus projects radially into the circumferential intermediate space between two adjacent magnet elements 7.

[0042] Furthermore, the burst protection sleeve 8 is equipped with an insertion aid / assembly aid. For this purpose, the burst protection sleeve 8 is implemented with a diameter change, in which case the (inner) diameter increases as it approaches the second axial end 12b of the burst protection sleeve. In Figure 7As can be seen, each covering section 9 is adjacent to an axial extension 13 which extends in the axial direction inclined to the covering section 9. At the same time, the depth of the recess 11 decreases towards the second end 12b. Thus, each recess 11 / bridge region 10 has a tapered rising side 14 towards the second end 12b( Figure 7 ). The extension 13 and the side 14 together form a tapered expanding annular edge 15 at the second axial end 12b of the burst protection sleeve 8, which realizes a diameter change. This further facilitates axially pressing the burst protection sleeve 8 onto a pre-assembly including the main part 5 and the magnet element 7.

[0043] Regarding the positioning of the rotor 4 relative to the stator 2, it can also be seen in Figure 2 that the annular edge 15 is arranged axially offset from the magnet element 7 and from the stator laminations 17, which minimizes eddy current losses during operation of the electric motor 1 as much as possible. This results in an air gap 24 of constant thickness in the radial region between the stator laminations 17 and the outer peripheral side of the burst protection sleeve 8.

[0044] The burst protection sleeve 8 is preferably made of stainless steel.

[0045] Thus, the electric motor 1, preferably implemented as a brushless DC electric motor, is equipped with a rotor 4 which is preferably implemented in a way that is completely adhesive-free, i.e., in particular without adhesion to the magnet element 7.

[0046] In other words, according to the invention, the special protrusion geometry in the burst protection sleeve 8 between the magnets 7 is used to locally reduce the stiffness of the burst protection sleeve 8 at the circumference of the magnets 7 (in the tangential direction). Thus, in the case of applying a relatively high press-fit force 16 to the rotor magnets 7 on the rotor carrier 5 / rotor lamination stack, a smaller force is used to assemble the sleeve 8.

[0047] Figures 11 to 13 are an isometric view and a sectional view of a BLDC rotor 4 having surface magnets 7 and a burst protection sleeve 8 without adhesively bonding the magnets 7 to the BLDC stator 2. The assembly of the rotor 4 includes a rotor carrier 5, rotor magnets 7 and a burst protection sleeve 8. The rotor carrier 5 is typically designed as a stamping stack having a number of electrical sheets. Alternatively, the rotor carrier 5 is designed as a sintered part made of a powder core material with low eddy current losses. If eddy current losses are not particularly critical for the design of the BLDC motor 1, the rotor carrier 5 can generally be made of a ferromagnetic material (e.g., steel). The rotor magnets 7 are typically designed as sintered NdFeB (rare earth material) magnets. Alternatively, the magnets 7 are designed as sintered parts made of hard ferrite. The burst protection sleeve 8 is preferably made of stainless steel as a deep-drawn part.

[0048] The preferred assembly sequence of the BLDC rotor 4 is as follows: 1) Form a stamping stack (stamp and stack) to form the rotor carrier 5; 2) Attach the rotor magnets 7 to the stamping stack 5, where the magnets 7 are held by a device, or the stamping stack 5 is slightly magnetized such that the magnets 7 are attracted; 3) Attach the burst protection sleeve 8 to the subassembly including the rotor carrier 5 (stamping stack) and the magnets 7; in this regard, the sleeve 8 is pushed on, where the rotor magnets 7 are axially supported in the assembly device.

[0049] Figures 8 to 10 is an isometric view and a sectional view of the described BLDC rotor 4. According to the invention, the grooves 10, 11 / local protrusions are arranged on the circumference of the burst protection sleeve 8 and are located axially between the rotor magnets 7 along the sleeve 8. These geometries locally reduce the stiffness of the sleeve 8 and, accordingly, the assembly force. Thus, even at relatively low forces and / or with higher tolerances of the subassembly, the burst protection sleeve can be mounted as a press fit 16 on the subassembly including the rotor carrier 5 (lamination stack) and the magnets 7. In mass production, the press fit typically has a tolerance of at least 0.2 mm to 0.3 mm or more while maintaining all tolerances. In this case, it is practically impossible to achieve this with a cylindrical steel sleeve (the assembly force of the cylindrical steel sleeve and the supercritical stresses in the sleeve 8 / magnets 7 due to mechanical loads are too high). The protrusions 10 in the sleeve geometry between the rotor magnets 7 allow for a local reduction in stiffness in the tangential direction at the circumference of the sleeve 8. Thus, the assembly force is relatively low, and the mechanical stresses in the sleeve 8 and the magnets 7 are at an acceptable level after assembly.

[0050] The burst protection sleeve 8, which is pushed on as a press fit 16, presses the rotor magnets 7 onto the rotor carrier 5. Since the magnets 7 do not have to be glued in this case, there is no need to provide a bonding gap between the ferromagnetic circuits of the magnetic path between the rotor carrier 5 and the rotor magnets 7. This provides the following advantage in terms of reluctance: the magnetic field closes more efficiently in the region of the rotor carrier 5. Using the geometry of the protrusions 10, the sleeve thickness, and the tolerance of the press fit 16, the sleeve 8 can be dimensioned such that the sleeve fixes and fastens the rotor magnets 7 to the rotor 4 against all critical thermo-mechanical loads, dynamic loads, and vibration loads by means of a frictional connection (radially inward sleeve pressure).

[0051] Figures 4 to 7An isometric view and a sectional view of the burst protection sleeve 8 are shown. To facilitate the installation of the burst protection sleeve 8 on the subassembly of the rotor carrier 5 (rotor lamination stack) and the magnet 7, an insertion area (annular edge 15) is provided, where the magnet 7 is inserted into the sleeve 8 or the sleeve 8 is pushed onto the magnet 7 when the press fit 16 is established. The advantage of this assembly aid geometry of the sleeve 8 is that in one of the two ends 12b of the sleeve 8, a tapered transition to a flat area bent axially to a metal strip is produced by a deep drawing process. This transition is usually laterally cut further from the metal strip towards the flat area in a stamping and deep drawing machine. In this case, the transition that would normally be cut in the case of a cylindrical stamping part is used as the insertion area for assembly.

[0052] Figures 1 to 3 An isometric view and a sectional view of an assembly including the stator 2 and the rotor 4 are also shown. The stator 2 generally includes a stator lamination stack 20, a pole shoe isolation component, a winding 19 including a circuit and a contact interface, and a overmolding 26 of the stator 2 (the overmolding is generally used to protect the winding 19 and electrical contacts since the overmolding is arranged in a space filled with a medium, such as in a pump application of the BLDC - E motor 1).

[0053] The insertion area 15 for mounting the burst protection sleeve 8 ( Figures 1 to 3 ) is axially arranged in the space between the rotor 4 and the stator 2 of the BLDC electric motor 1, where the geometry does not cause any negative impact on the mechanical air gap 24 between the stator 2 and the rotor 4. The mechanical air gap 24 between the stator 2 and the rotor 4 of the motor 1 should be kept as small as possible to improve the efficiency of the motor 1.

[0054] Explanation of reference numerals

[0055] 1 Electric motor 2 Stator 3 Axis of rotation 4 Rotor 5 Main part 6 Side 7 Magnet element 8 Burst protection sleeve 9 Cover section 10 Bridging area 11 Depression 12a First end 12b Second end 13 Extension 14 Side surface 15 Annular edge 16 Press fit 17 Stator lamination 18 Stator carrier 19 Winding 20 Stack 21 Outer surface 22 Distance 23 Protrusion 24 Air gap 25 Pole shoe isolation component 26 Overmolding.

Claims

1. An electric motor (1), comprising a stator (2) and a rotor (4) rotatably mounted relative to the stator (2) about a rotational axis (3), wherein, the rotor (4) further has: a main part (5); a plurality of magnet elements (7) which are distributed along a circumferential direction and are received on a radial surface (6) of the main part (5) in a spaced-apart manner; and a burst protection sleeve (8) which covers the main part (5) and the magnet elements (7), and wherein the burst protection sleeve (8) has: a plurality of covering sections (9), each of which directly contacts a magnet element (7); and a plurality of bridging regions (10) which connect two adjacent covering sections (9) together, characterized in that the burst protection sleeve (8) is used to directly support the magnet elements (7) relative to the main part (5), so that there is no need to provide an adhesive gap between ferromagnetic circuits of a magnetic path between the main part (5) and the magnet elements (7), wherein the bridging regions (10) have a lower bending strength in the circumferential direction than the covering sections (9), the burst protection sleeve (8) has a diameter change at an axial end (12b), at the axial end (12b) of the burst protection sleeve (8), each covering section (9) has an extension (13) which protrudes obliquely in the axial direction, and each bridging region (10) has a tapered rising side surface (14) near the axial end (12b), and the extension (13) and / or the tapered rising side surface (14) form the diameter change.

2. The electric motor (1) according to claim 1, characterized in that the burst protection sleeve (8) is fixed to the magnet elements (7) attached to the main part (5) by means of a press fit (16).

3. The electric motor (1) according to claim 1 or 2, characterized in that the corresponding bridging region (10) has a recessed portion (11) in a groove shape.

4. The electric motor (1) according to claim 1 or 2, characterized in that the corresponding bridging region (10) is open towards one axial end (12a) or two axial ends (12a, 12b) of the burst protection sleeve (8).

5. The electric motor (1) according to claim 1, characterized in that the diameter change is formed by a tapered widened annular edge (15), and the extension (13) and the tapered rising side surface (14) together form the tapered widened annular edge (15).

6. The electric motor (1) according to claim 1, characterized in that the rotor (4) is arranged relative to the stator (2) such that the extension (13) is axially adjacent to the magnet element (7).

7. The motor (1) according to claim 1 or 2, characterized in that the motor (1) is designed as a brushless DC electric motor.

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