Rotor for an electric machine and method for its manufacture

Abstract

Rotor (10) for an electric machine, with the following features: - the rotor (10) comprises an inner lamination stack (12) and an outer lamination stack (14), - the rotor (10) contains an inner magnet (13) aligned along a secant of its cross-section and another inner magnet (13), - the inner magnets (13) are oriented at obtuse angles to each other and symmetrically to a radius of the cross-section and - the rotor (10) has a cavity extending between the inner magnets (13) and carries an outer magnet (15) and a bandage (11) spanning the outer magnet (15), characterized by the following features: - the rotor (10) has a pretensioning element (20) arranged radially below the outer magnet (15) for tightening the bandage (11), namely a wedge (20) directed towards the outer magnet (15) within the cavity, and - the inner magnet (13) is embedded between the laminated stacks (12, 14) in such a way that the wedge (20) acts on the bandage (11) via the inner magnet (13).

Description

[0001] The present invention relates to a rotor for an electric machine. The present invention further relates to a corresponding manufacturing method, a corresponding electric machine, and a corresponding motor vehicle. State of the art

[0002] IEC 60034-16-1 standardizes different types of excitation for single-phase and three-phase synchronous machines. Synchronous machines of small to medium power, such as those used as servomotors in automotive engineering, are predominantly permanently excited (permanently excited synchronous machines, PSMs) according to the state of the art. The magnets used for this purpose are mounted on or incorporated into the rotor's laminated cores in a variety of ways.

[0003] Well-known magnets include surface-mounted and embedded ("buried") magnets, which are often arranged in a star configuration within the rotor to concentrate the flux. To further increase the flux density in the air gap, rare-earth magnets in particular are often arranged in a V-shape beneath a pole. In the pursuit of a compromise between the lowest possible magnetic edge scattering and manageable tensile and shear stresses, both configurations are sometimes combined.

[0004] To secure the surface magnets of fast-rotating rotors, they are usually equipped with a reinforcement that absorbs the centrifugal force acting on the magnets during operation. In high-performance motors, thin-walled bandages made of fiber-reinforced plastic are used instead of metal sleeves to prevent eddy currents in the reinforcement.

[0005] In the design and manufacture of banded rotors, a deliberately defined overlap of the laminated core and rotor bandage components is required with regard to operational functionality.

[0006] The drum must therefore always be “tightened” for operation under all load collectives.

[0007] The required preload is achieved using state-of-the-art technology through a geometric transition or interference fit. The overlap between the lamination stack and the bandage is typically less than 1 percent of the rotor diameter.

[0008] This makes the joining process challenging, as for damage-free and contactless assembly, the components must necessarily be joined below ambient temperature or under contact (which places high demands on the respective surfaces). For this purpose, the laminated core is subjected to intense cooling – for example, with nitrogen – and its outer surface is finely ground.

[0009] US 2014 / 0 009 024 A1 discloses a rotor of an electric motor, wherein the rotor has a rotor base body, a plurality of magnets arranged on an outer circumferential surface of the rotor base body and a bandage.

[0010] DE 10 2004 046 440 A1 discloses a rotor of an electric motor, comprising a rotor base body, a plurality of magnets arranged on an outer circumferential surface of the rotor base body and a bandage, wherein a clamping device is provided for aligning the rotor base body on a rotor shaft.

[0011] US 2016 / 0 028 282 A1 discloses a rotor of an electric motor, wherein the rotor has a rotor base body, a plurality of magnets arranged on an outer circumferential surface of the rotor base body and a bandage, wherein an end element is arranged on at least one axial end of the rotor base body, which end element is arranged radially between the bandage and an edge magnet.

[0012] DE 102 16 856 A1 discloses a rotor of an electric motor, wherein the rotor has a rotor base body, a plurality of magnets arranged on an outer circumferential surface of the rotor base body and a bandage, wherein a retaining ring is provided for fixing each of the two axial ends of the bandage.

[0013] Further prior art can be found in the documents DE 10 2005 041 676 A1, DE 10 2017 223 042 A1, DE 10 2010 022 702 A1, DE 10 2010 062 393 B4, DE 10 2013 102 822 A1, WO 2014 / 125 433 A2, DE 10 2019 117 686 A1, DE 101 31 474 A1, JP 2013- 116 002 A, DE 11 2010 005 756 T5 and CN 2 05 377 495 U. Disclosure of the invention

[0014] The invention provides a rotor, a method for its manufacture, an electric machine and a motor vehicle according to the independent claims.

[0015] The invention is based on the idea of ​​providing a generic rotor with additional components or supplementary geometric features on existing components to generate the radial preload.

[0016] This approach provides rotors according to the invention with high operational stability and speed.

[0017] Further advantageous embodiments of the invention are specified in the dependent patent claims. Thus, the said components can optionally already be present as stamped tabs or other spring elements on the components used, or they can be introduced as additional radially or axially inserted elements during pre- or post-processing during assembly.

[0018] One advantage of this approach is the reduction of complex pre-processes—such as grinding the outer diameter of the rotor cores—and cold-hot processes in production. Rather, the production of a rotor according to the invention is achieved sustainably through resource-saving processes. Short description of the drawings

[0019] Embodiments of the invention are illustrated in the drawings and are described in more detail below. Fig. 1 shows the state of the art. Fig. 2 shows inventive embodiments of existing components. Fig. 3 shows additional components according to the invention for insertion before, during or after assembly. Embodiments of the invention

[0020] Fig. Figure 1 shows a cross-sectional view of a segment of a bandaged rotor (10). The segment consists of an inner (12) and outer laminated core (14) enclosing two magnets (13) aligned at an obtuse angle to each other and symmetrically to the rotor radius. Together, the magnets (13) thus form the shape of the letter "V." The outer laminated core (14) additionally supports an outer magnet (15), which in turn is spanned by the bandage (11) of the rotor (10).

[0021] The term "bandage" should be interpreted in a broad sense, including reinforcements wound directly onto the rotor (10) as well as inherently strong components for securing the loose outer laminated core (14) and magnets (15). If this bandage (11) does not fit tightly against the rotor (10), it lacks sufficient strength, and failure occurs during its rapid rotation, as the figure clearly demonstrates. This type of component design therefore presents the expert with the challenge of generating a prestress in the bandage (11).

[0022] Fig. Figure 2 illustrates the corresponding segment of a rotor (10) according to the invention that addresses this challenge. For this purpose, the electrical sheets of the laminated cores (12, 14) were laser-cut or punched during production in such a way that they each have a tab (20) on their surface facing the inner magnet (13), which is received in a corresponding groove in the magnet. The tabs (20), shown here in the untensioned state after punching or cutting, are tensioned during assembly so that, after final assembly, they tighten the bandage (11) over the inner magnet (13).

[0023] Fig. 3 illustrates a variation of this principle, in which instead of the molded tabs (20 - Fig.2) a wedge (20) manufactured independently of the laminated cores (12, 14) serves as a prestressing element, which—pointing radially outward with respect to the rotor (10) and thus in the direction of the outer magnet (15)—is arranged in the cavity between the inner magnets (13) and thus at the apex of the letter "V" formed by the latter. Such a wedge (20) may optionally be inserted during assembly or subsequently inserted longitudinally into the cavity of the rotor (10) without departing from the scope of the invention.

Claims

[1] Rotor (10) for an electrical machine, having the following features: - the rotor (10) comprises an inner laminated core (12) and an outer laminated core (14), - the rotor (10) contains an inner magnet (13) aligned along a secant of its cross-section and another inner magnet (13), - the inner magnets (13) are aligned at an obtuse angle to each other and symmetrically to a radius of the cross-section and - the rotor (10) has a cavity extending between the inner magnets (13) and carries an outer magnet (15) and a bandage (11) spanning the outer magnet (15), characterized by following features: - the rotor (10) has a pretensioning element (20) arranged radially below the outer magnet (15) for tightening the bandage (11), namely a wedge (20) directed towards the outer magnet (15) within the cavity, and - the inner magnet (13) is embedded between the laminated cores (12, 14) in such a way that the wedge (20) acts on the bandage (11) via the inner magnet (13). [2] Method for producing a rotor (10) according to claim 1, characterized by following features: - Electrical sheet is cut or punched and assembled into the laminated cores (12, 14) and - the sheet packages (12, 14) and magnets are mounted and reinforced with the bandage (11). [3] Method according to claim 2, characterized by following features: - the wedge (20) is formed during cutting or punching on the electrical sheet and - the wedge (20) is tightened during assembly. [4] Method according to claim 2, characterized by following features: - the wedge (20) is manufactured independently of the lamination stacks (12, 14) and - the wedge (20) is inserted during assembly or inserted lengthwise into a cavity of the rotor (10) remaining after assembly. [5] Electric machine with a rotor (10) according to claim 1. [6] Motor vehicle with an electric machine according to claim 5.

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