Rotor for an electric motor and method for manufacturing such a rotor

Abstract

Rotor for an electric motor with a rotor shaft (10) and a magnetic ring (11) and an adhesive layer (20, 24, 26, 28) which is arranged between the rotor shaft (10) and the magnetic ring (11) and surrounds the magnetic ring (11) radially and axially, wherein the magnetic ring (11) is formed by several axially arranged magnetic ring sections (12, 14, 16), wherein the adhesive layer (24) radially surrounding the magnetic ring (11) completely limits the rotor in the axial section in which the magnetic ring (11) is arranged, and wherein axial grooves (34) and / or radial grooves (36) are formed on the rotor shaft (10) through which adhesive can be introduced into a gap (18) between the rotor shaft (10) and the magnetic ring (11).

Description

[0001] The invention relates to a rotor for an electric motor with a rotor shaft and a magnetic ring as well as an adhesive layer which is arranged between the rotor shaft and the magnetic ring and surrounds the magnetic ring radially and axially.

[0002] Electric motor rotors are typically formed by laminated cores containing openings for permanent magnets. Single-piece rotors with openings for the magnets are also known. When these electric motors are used in the high-speed range, it is necessary for the rotor, and any additional masses driven by it, to be accelerated to speeds of over 80,000 rpm in the shortest possible time, as is particularly necessary when driving electric compressors in internal combustion engines. To achieve this, it is necessary to use rotors that are as small as possible to be accelerated, as these have a lower moment of inertia.

[0003] For this reason, electric motors have become popular that no longer have laminated cores or other magnet carriers, but in which the magnets are attached directly to the rotor shaft of the electric motor. However, this requires that the magnets be sufficiently firmly attached to the shaft to prevent them from becoming detached from the rotor shaft. Furthermore, the extremely high centrifugal forces exerted may cause magnet pieces to break out of the segments over time. Axial displacement of the magnet ring must also be prevented.

[0004] An electric motor that fulfills these tasks is disclosed, for example, in DE 36 22 231 A1. In this electric motor, a magnetic ring is arranged on a stepped rotor shaft along its largest circumference. The magnetic ring is surrounded by a thin plastic layer that fills a gap between the inner rotor shaft, a radially outer sleeve, and two axially limiting end rings. While the sleeve is designed to absorb the centrifugal forces, the end rings secure the magnet against axial displacement.

[0005] A similar rotor is also known from US 2012 / 0 049 662 A1. In this rotor, however, the existing gaps between the magnets and the rotor shaft, the outer sleeve, and the two end plates are filled with an adhesive. The connection between the end plates and the magnets is created in a different manufacturing step than the connection of the magnets to the rotor shaft and the outer sleeve.

[0006] In addition, DE 87 16 646 U1 discloses a single-phase motor whose rotor has two magnetic half-shells that are mounted radially offset from one another on a shaft by being overmolded with a plastic.

[0007] However, these electric motors have the disadvantage that they require a relatively large number of manufacturing steps, and the size of the components used must be coordinated. This number of components, designed to increase durability or balance such a rotor, also increases the size and weight of these rotors.

[0008] Further rotors are known from DE 10 2010 062 385 A1, JP 2014- 121 192 A and JP 2013- 223 403 A.

[0009] The task therefore arises of providing a rotor for an electric motor and a method for its production that can be accelerated to high speeds in the shortest possible time, as is required when using an electric motor for an electric compressor in an internal combustion engine, without the risk of the permanent magnets becoming loose. The rotor should be manufactured in as few process steps as possible, have few components, and be lighter than known designs. Imbalances in the rotor should be able to be compensated for without additional components.

[0010] This object is achieved by a rotor for an electric motor having the features of main claim 1 and a method for producing such a rotor having the features of claim 5.

[0011] Because the magnetic ring is formed by several magnetic ring sections arranged axially one behind the other, with the adhesive layer radially surrounding the magnetic ring completely radially defining the rotor in the axial section in which the magnetic ring is arranged, and with axial grooves and / or radial grooves being formed on the rotor shaft through which adhesive can be introduced into a gap between the rotor shaft and the magnetic ring, additional components can be dispensed with, thereby reducing weight and simplifying assembly. The adhesive layer secures the magnet axially and radially to the rotor shaft. In addition, the surrounding adhesive layer prevents magnetic material from breaking out of the magnetic ring and additionally protects the magnetic ring against externally attacking media. At the same time, assembly is made easier due to lower resistance when sliding the magnetic rings onto the shaft.This also facilitates the even distribution of the adhesive and thus ensures full-surface bonding.

[0012] The object is accordingly protected by a method for producing such a rotor, in which first the rotor shaft and the magnetic ring are aligned axially and radially to one another, wherein at least one radial gap is formed between the magnetic ring and the rotor shaft, into which gap an adhesive is introduced before or after the alignment of the magnetic ring to the rotor shaft, then the rotor shaft with the adhesive-attached magnetic ring is placed in a mold and fastened, wherein a radial gap is formed between the magnetic ring and the radially surrounding mold wall and an axial gap is formed between the axially delimiting mold walls and the axial ends of the magnetic ring, an adhesive is selected which does not bond to the mold wall and then the selected adhesive is introduced into the mold, the gaps being completely filled by the adhesive.Finally, the adhesive is cured to create an adhesive layer, and the mold is removed from the rotor. This process allows a fully encapsulated rotor with minimal weight and high strength, even suitable for high centrifugal forces, to be created in just a few manufacturing steps.

[0013] Preferably, the adhesive layer surrounding the magnetic ring axially limits the rotor radially outside the rotor shaft. Additional end plates can thus be eliminated without compromising strength. Shifting of the magnetic ring on the shaft is prevented, creating complete encapsulation.

[0014] In a further embodiment of the invention, the adhesive layer axially defining the rotor is thicker than the adhesive layer radially defining the rotor. This allows the rotor to be balanced via the axially defining adhesive layer by creating holes or recesses in the axially defining adhesive layers.

[0015] Accordingly, the adhesive layer axially surrounding the rotor has recesses to ensure true rotation of the rotor. This eliminates the need for additional balancing weights.

[0016] In a further development of the method according to the invention, the rotor is first clamped in a balancing machine after its manufacture and then the adhesive layer axially adjacent to the magnetic ring is machined to balance the rotor, whereby reliable concentricity of the rotor is achieved in a simple manner.

[0017] This creates a rotor for an electric motor that can achieve very high accelerations thanks to a very low moment of inertia. Despite the forces generated during these accelerations, the connection between the rotor shaft and the magnets exhibits excellent durability without the need for additional components to secure the magnets. This durability is further enhanced by additional measures. Rotor imbalances can be easily compensated for. Material detachment from the magnetic ring is reliably prevented, as is the detachment of a ring magnet within the surrounding layer. The number of manufacturing steps and the number of components to be assembled are reduced.

[0018] An embodiment of a rotor according to the invention for an electric motor and a method for producing such a rotor is shown in the figures and is described below.

[0019] The Fig. 1 shows a side view of a rotor according to the invention for an electric motor of an electric compressor in a sectional view.

[0020] The Fig. 2 shows a sectional view of the rotor according to the invention from Fig. 1 in a first manufacturing step.

[0021] The Fig. 3 shows a sectional view of the rotor according to the invention from Fig. 1 in a second manufacturing step.

[0022] The rotor of an electric motor according to the invention shown in the figures consists of a rotor shaft 10 and a magnetic ring 11 fastened to the rotor shaft 10, which consists of three magnetic ring sections 12, 14, 16 and can be arranged radially inside a stator (not shown) with stator windings in a known manner after its manufacture.

[0023] An adhesive layer 20 is formed in a radial gap 18 between the rotor shaft 10 and the magnetic ring 11, via which the magnetic ring 11 is firmly connected to the rotor shaft 10. The magnetic ring sections 12, 14, 16 lie axially directly on top of one another and are connected to one another by the adhesive layer 20 and a radially outer adhesive layer 24, which completely radially surrounds the magnetic ring sections 12, 14, 16. This adhesive layer 24 has a connection to two adhesive layers 26, 28, which axially delimit the magnetic ring 11 on the rotor shaft 10, so that the magnetic ring 11 as a whole and each individual magnetic ring 12, 14, 16 is completely surrounded by an adhesive layer 20, 24, 26, 28.

[0024] By encapsulating the magnetic ring 11 with adhesive on the rotor shaft 10, all magnetic ring sections 12, 14, and 16 are secured against both radial and axial loosening. Furthermore, the breakout of magnetic material from the magnetic ring sections is prevented, even at high rotational speeds. Furthermore, the rotor is completely protected against external influences such as corrosive gases or liquids.

[0025] Such a rotor is manufactured by first sliding the magnetic ring 11 or the magnetic ring sections 12, 14, 16 onto the rotor shaft 10 in a corresponding holding device 30 and positioning them axially and radially to the rotor shaft 10. In this position, there is a small air gap 18 between the inner diameter of the magnetic ring 11 and the outer diameter of the rotor shaft 10, and the axially opposite magnetic ring sections 12 and 14, or 14 and 16, rest on one another. In this position, adhesive is filled into the gap 18. Depending on the viscosity of the adhesive used and the size of the gap 18, it may be useful to form one or more axial grooves 34 or radial grooves 36 on the rotor shaft 10, as shown in Fig.2 is shown with dashed lines. In this exemplary embodiment, the axial groove 34 on the rotor shaft 10 runs over the entire length of the magnetic ring 11. In the central region of each magnetic ring section 12, 14, 16, a radial groove 36 is additionally formed on the rotor shaft 10. The adhesive can be distributed along the rotor shaft 10 via these grooves 34, 36, so that a full-surface adhesive layer 20 is created between the rotor shaft 10 and the magnetic ring 11.

[0026] Alternatively, it is also possible to first apply the adhesive to the rotor shaft 10 and distribute it evenly and then slide on the magnetic ring 11 or the magnetic ring sections 12, 14, 16 and align them correctly.

[0027] In both designs, a certain stability of the connection between the magnetic ring 11 and the rotor shaft 10 is initially created. The rotor shaft 10 with the magnetic ring 11 is then fastened via the rotor shaft 10 in a mold 38. The mold tightly encloses the rotor shaft 10 on both sides, specifically at a small distance from the magnetic ring 11. Accordingly, after the mold 38 is closed, an axial gap 41 is created between the mold walls 40 that axially delimit the mold 38 to the mold space and the axial ends of the magnetic ring 11. The mold wall 42 arranged radially around the magnetic ring is also arranged at a uniform distance from the magnetic ring 11, so that a radial gap 44 is created that surrounds the magnetic ring 11. The radial gap 44 is smaller than the axial gap 41. After closing the mold 38, adhesive is introduced into the mold until the entire gaps 41, 44 between the mold walls 40, 42 and the magnetic ring 11 are filled.The materials of the mold walls 40, 42 and the adhesive must be matched to one another in such a way that no connection is created between the adhesive and the mold walls 40, 42, but the rotor as a whole with the radially and axially surrounding adhesive layers 24, 26, 28 can be easily removed from the mold 38 after opening.

[0028] The entire rotor is then cured, which can take place in an oven or by simple aging or light curing, whereby a high strength of the adhesive layers 20, 24, 26, 28 is achieved, which now act as a one-piece adhesive layer.

[0029] Finally, the rotor can be checked for correct concentricity in a balancing machine. To achieve this concentricity, the axially limiting adhesive layers 26, 28 must be sufficiently thick so that they can be machined for balancing. This can be done by either removing layers or, for example, by making short holes as recesses 46 in these adhesive layers 26, 28 until the rotor is completely concentric.

[0030] This creates a rotor for an electric motor in which a large-area bond is ensured with sufficient adhesive, so that despite the high centrifugal forces that occur, the magnets can be attached without additional components, while the rotor still maintains high speed stability. Since the rotor, apart from the magnets, has no large masses that need to be accelerated, the inertial forces are minimized, which enables rapid start-up of the electric motor. This compensates for any imbalance in the rotor. The production of such an encapsulated rotor, which is thus insensitive to external influences, is possible with a small number of parts to be manufactured and a small number of necessary production steps.

[0031] It should be clear that various design variants are possible compared to the described embodiment within the scope of the main claim. For example, instead of the three magnetic ring sections described, a single magnetic ring can be applied to the rotor shaft, or any number of axially adjacent magnetic ring sections can be applied, or the rotor shaft can be manufactured with or without grooves. Segmented, partially annular magnetic elements can also be used.

Claims

[1] Rotor for an electric motor with a rotor shaft (10) and a magnetic ring (11) and an adhesive layer (20, 24, 26, 28) which is arranged between the rotor shaft (10) and the magnetic ring (11) and surrounds the magnetic ring (11) radially and axially, wherein the magnetic ring (11) is formed by a plurality of magnetic ring sections (12, 14, 16) arranged axially one behind the other, wherein the adhesive layer (24) radially surrounding the magnetic ring (11) completely delimits the rotor in the axial section in which the magnetic ring (11) is arranged, and wherein axial grooves (34) and / or radial grooves (36) are formed on the rotor shaft (10), via which adhesive can be introduced into a gap (18) between the rotor shaft (10) and the magnetic ring (11). [2] Rotor for an electric motor according to claim 1, characterized by that the adhesive layer (26, 28) axially surrounding the magnetic ring (11) axially limits the rotor radially outside the rotor shaft (10). [3] Rotor for an electric motor according to one of the preceding claims, characterized by that the adhesive layer (26, 28) axially delimiting the rotor (10) is thicker than the adhesive layer (24) radially delimiting the rotor. [4] Rotor for an electric motor according to one of the preceding claims, characterized by that the adhesive layer (24, 26) axially delimiting the rotor has recesses (46) for producing a concentric running of the rotor. [5] Method for producing a rotor for an electric motor according to one of the preceding claims, characterized by , that the rotor shaft (10) and the magnetic ring (11) are aligned axially and radially with respect to one another, wherein at least one radial gap (18) is formed between the magnetic ring (11) and the rotor shaft (10), into which an adhesive is introduced before or after the alignment of the magnetic ring (11) with respect to the rotor shaft (10), then the rotor shaft (10) with the glued-on magnetic ring (11) is inserted into a mold (38) and fixed, wherein a radial gap (44) is formed between the magnetic ring (11) and the radially surrounding mold wall (42) and an axial gap (41) is formed between the axially delimiting mold walls (40) and the axial ends of the magnetic ring (11), an adhesive is selected which does not bond to the mould wall (40, 42), the selected adhesive is introduced into the mold (38), the gaps (41, 44) being completely filled by the adhesive, finally the adhesive is cured to produce an adhesive layer (20, 24, 26, 28) and the mold (38) is removed from the rotor. [6] A method for producing a rotor for an electric motor according to claim 5, characterized by , that the rotor is clamped into a balancing machine, the adhesive layer (26, 28) axially adjacent to the magnetic ring (11) is machined to balance the rotor.

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