DE102020124652A1 - radial flux machine - Google Patents

Abstract

The invention relates to a radial flow machine (1), comprising a rotor (2) with a rotor body (22) arranged on a rotor shaft (21) and a stator (3), the rotor (2) having at least one bearing (4) relative to the Stator (3) is rotatably mounted. According to the invention, a dielectric (23) is arranged between the rotor body (22) and the rotor shaft (21), so that the rotor body (22) and the rotor shaft (21) are electrically insulated from one another in such a way that a rotor-shaft capacitance (CRotor_Welle) predetermined capacitance is formed, which reduces an electrical voltage existing between the bearing inner raceway and the bearing outer raceway to a predetermined voltage level.

Description

The present invention relates to a radial flux machine, comprising a rotor with a rotor body arranged on a rotor shaft and a stator, the rotor being rotatably mounted relative to the stator via at least one bearing.

For the bearings of an electric motor, in addition to the mechanical wear caused by shaft rotation, electrical currents that flow through the bearings from the rotor shaft to ground are another reason for wear. A certain magnitude of stress can overcome the insulating properties of bearing lubrication, creating sparks that can lead to pitting, ridged surfaces, fusion craters and eventually premature bearing and motor failure. A bearing stress, i. H. the stress between the two bearing shells usually correlates with a shaft stress, i. H. the voltage between the shaft and ground.

Due to the capacitive coupling between the stator winding and the rotor and the high-frequency activation of the stator phases, a voltage potential forms at the rotor bearings, which can damage the bearings by means of so-called discharge currents through the bearings. As countermeasures, for example, the bearings are isolated (e.g. using ceramic balls) or the shaft is grounded using a grounding contact (electrically parallel to the bearings).

From the DE 10 2017 109 049 A1 a device and a method for compensating for a shaft voltage on a shaft are also already known. In this case, the compensation voltage is coupled directly or indirectly to the rotor shaft via a coupling element by means of a compensation circuit for generating a compensation voltage. The shaft voltage is detected directly or indirectly on the rotor shaft via a pickup element.

The object of the invention is to provide a radial flux machine in which the shaft voltage and thus the bearing currents that occur are reduced.

This object is achieved by a radial flux machine with the features of patent claim 1. The radial flux machine according to the invention is in particular an electrical machine in a motor vehicle - in particular an electrical machine designed as a traction machine to drive the motor vehicle electrically or with electrical assistance or an electrical machine in the form of a clutch, a steering or other actuators to drive. A radial flux machine according to the invention comprises a rotor with a rotor body arranged on a rotor shaft and a stator, the rotor being rotatably mounted relative to the stator via at least one bearing. According to the invention, a dielectric is arranged or formed between the rotor body and the rotor shaft, so that the rotor body and the rotor shaft are electrically insulated from one another in such a way that a rotor-shaft capacitance of a predetermined capacitance is formed, which is above the at least one bearing for supporting the Electrical voltage occurring on the rotor shaft is limited to a predetermined voltage level or reduced accordingly in comparison to an embodiment without a dielectric.
This has the advantage that the voltage (or voltage potential) applied across the bearing is reduced, so that the probability of spark discharges is reduced and the energy / power of the discharges that still occur is limited with the result that the bearing damage due to electrical discharges be reduced.

Further advantageous refinements of the invention are specified in the dependently formulated claims. The features listed individually in the dependent claims can be combined with one another in a technologically meaningful manner and can define further refinements of the invention. In addition, the features specified in the claims are specified and explained in more detail in the description, with further preferred configurations of the invention being presented.

According to an advantageous embodiment of the invention, it can be provided that the predetermined rotor-shaft capacitance formed between rotor body and rotor shaft is dimensioned such that it is less than or equal to the shaft-mass capacitance formed between rotor shaft and ground.

The rotor-shaft capacitance formed between the rotor body and the rotor shaft is particularly preferably at most fifty percent of the rotor-mass capacitance formed between the rotor body and the mass. In this case, the rotor-mass capacitance is essentially characterized by the winding-rotor capacitance formed between the winding and the rotor body and the rotor-stator capacitance formed between the rotor body and the stator.

According to a further preferred further development of the invention, it can also be provided that the dielectric has a permeability which is dimensioned in such a way that it approximately corresponds to the permeability of air, in particular has a relative permeability which is twice the permeability of air, especially preferred the 1.5 times the permeability of air and most preferably corresponds to 1.1 times the permeability of air.
It can hereby be achieved that with given geometric framework conditions, the capacitance formed between the rotor body and the shaft can be made as small as possible.

Furthermore, according to a likewise advantageous embodiment of the invention, provision can be made for the dielectric to be formed at least predominantly by air, which enables a structurally simple and space-saving construction and no filling material and associated process for introducing the filling material is required. According to an alternative embodiment of the invention, it can be provided that the dielectric is formed at least predominantly by polystyrene foam. This material is also easy to process and offers significant advantages both with regard to the electrically insulating properties and with regard to mechanically supporting properties.

Furthermore, the invention can also be further developed such that the rotor body is arranged at a distance from the rotor shaft in an electrically insulated manner by at least one connector element designed to be electrically insulating. The at least one connector element is preferably designed in such a way that the rotor body is held in a centered, coaxial manner at a distance from the rotor shaft.
In this way it can be achieved that a constructively simple and cost-effective possibility is found for aligning the rotor body with respect to the rotor shaft and at the same time electrically isolating it with respect to the rotor shaft.

The invention is preferably used in radial flow machines with a speed range of up to 60,000 rpm, particularly preferably up to 45,000 rpm and very particularly preferably up to 30,000 rpm.

The rotor can advantageously have a first connector element designed as a rotor body clamping ring at its first axial end of the rotor body and a second connector element designed as a rotor body clamping ring at its second axial end for insulating spacing of the rotor body and rotor shaft. In this way, in particular, simplified assembly of the rotor can be ensured.

The invention and the technical environment are explained in more detail below with reference to the figures. It should be pointed out that the invention should not be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and to combine them with other components and findings from the present description and/or figures. In particular, it should be pointed out that the figures and in particular the proportions shown are only schematic. The same reference symbols designate the same objects, so that explanations from other figures can be used as a supplement if necessary.

• 1 den Aufbau einer elektrischen Radialflussmaschine in einer möglichen Ausgestaltung der Erfindung in schematischer Darstellung in einem Axialschnitt, und
• 2 ein vereinfachtes kapazitives Ersatzschaltbild der in Figur dargestellten Radialflussmaschine.

Show it:

• 1 the structure of an electrical radial flow machine in a possible embodiment of the invention in a schematic representation in an axial section, and
• 2 a simplified capacitive equivalent circuit diagram of the radial flux machine shown in FIG.

1 shows the structure of an electrical radial flow machine 1 in a possible embodiment of the invention in a schematic representation in an axial section. The radial flow machine 1 shown comprises a rotor 2 with a rotor body 22 arranged in a rotationally fixed manner on a rotor shaft 21 and a stator 3, the rotor 2 being mounted axially on both sides via a bearing or roller bearing 4 designed as a ball bearing so that it can rotate relative to the stator 3. The rotor body 22 carries corresponding permanent magnets distributed over its circumference. A dielectric 23 is arranged between the rotor body 22 and the rotor shaft 21 . The dielectric 23 is designed in such a way that the rotor body 22 and the rotor shaft 21 are electrically insulated from one another in such a way that a rotor-shaft capacitance C _{rotor_shaft of a} predetermined capacitance is formed. The capacitance C _{rotor_shaft} is in turn dimensioned such that an electrical voltage occurring between the respective bearing 4 or between the bearing inner raceway and the bearing outer raceway of the respective bearing 4 during operation of the electrical machine 1 is reduced to a predetermined voltage level.

2 shows a simplified capacitive equivalent circuit diagram of in 1 shown and described above radial flux machine 1.
while in 1 A modified radial flux machine 1 is shown schematically in its mechanical structure, in which a dielectric 23 is added between the radially inner surface of the rotor body 22 and the rotor shaft 21, which electrically insulates the rotor surface from the rotor shaft 21 and has a capacitance (rotor-shaft capacitance C _{rotor shaft)} between rotor surface and rotor shaft 21 is in 2 the associated capacitive equivalent circuit diagram is shown.
The associated simplified capacitive replacement circuit diagram essentially shows two interconnected capacitive voltage dividers. A first voltage divider (voltage divider 1) is formed between a so-called common-mode voltage U _common-mode and ground and consists mainly of the series-connected capacitances C _winding - _rotor and C _rotor-stator (so-called C _{rotor_ground} ). A second voltage divider (voltage divider 2) is formed parallel to the rotor-stator capacitance C _rotor-stator and includes the rotor-shaft capacitance C _rotor-shaft newly created by the dielectric 23 as well as a shaft-ground capacitance C connected in series with it _{wave mass.} The shaft-mass capacitance C _shaft-mass consists essentially of a parallel connection of the two bearing capacitances C _{bearing_li} , C _{bearing_re} and a parallel-connected shaft geometry capacitance C _shaft geometry, with this capacitance in the geometry of the rotor shaft 21 in the Electrical machine 1 is formed or justified.

Since the newly created rotor-shaft capacitance C _rotor-shaft should have the smallest possible capacitance, the tap to the second voltage divider for the division factor of the first voltage divider is neglected for the sake of simplicity. The second voltage divider mainly consists of the rotor-shaft capacitance C _rotor-shaft and the bearing capacitances C _{bearing_li} , C _{bearing_re} . The shaft voltage U _shaft corresponds to the voltage across the bearing capacitances C _{bearing_li} , C _{bearing_re.} Due to the interconnection of the capacitive voltage dividers 1 and 2, their division factors are multiplied. For example, with a division factor of 7:1 for the first voltage divider and a factor of 20:1 for the second voltage divider, the total factor is 140:1. Assuming 280 volts as the common mode voltage, this results in a wave voltage of only approx. 2 volts.

The invention is not limited to the embodiments shown in the figures. The foregoing description is therefore not to be considered as limiting but as illustrative. The following patent claims are to be understood in such a way that a mentioned feature is present in at least one embodiment of the invention. This does not exclude the presence of other features. If the patent claims and the above description define 'first' and 'second' feature, this designation serves to distinguish between two similar features without establishing a ranking.

Reference List

1

radial flux machine

2

rotor

3

stator

4

camp

21

rotor shaft

22

rotor body

23

dielectric

24

connector element

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102017109049 A1 [0004]

Claims (10)

Radial flow machine (1), comprising a rotor (2) with a rotor body (22) arranged on a rotor shaft (21) and a stator (3), the rotor (2) having at least one bearing (4) relative to the stator (3) is rotatably mounted, characterized in that a dielectric (23) is arranged between the rotor body (22) and the rotor shaft (21), so that the rotor body (22) and the rotor shaft (21) are electrically insulated from one another in such a way that a rotor shaft -Capacity (C _{Rotor_welle} ) of a predetermined capacitance is formed, which reduces an electrical voltage (U _shaft ) occurring across the at least one bearing (2) during operation of the electrical radial flux machine (1) to a predetermined voltage level. Radial flow machine (1) according to claim 1 , characterized in that the predetermined rotor-shaft capacitance (C _{Rotor_Welle} ) formed between the rotor body () and the rotor shaft () is dimensioned in such a way that it is less than or equal to the shaft-mass capacitance formed between the rotor shaft () and ground (C _{wave_mass} ). Radial flow machine (1) according to one of the preceding claims , characterized in that the capacitance (C _{Rotor_Welle} ) formed between the rotor body (22) and the rotor shaft (21) is at most fifty percent of the rotor-mass capacitance (C _{Rotor_Masse} ) amounts to. Radial flow machine (1) according to one of the preceding claims, characterized in that the dielectric (23) has a permeability which is dimensioned such that it approximately corresponds to the permeability of air, in particular has a relative permeability which is twice the permeability of air, particularly preferably 1.5 times the permeability of air and very particularly preferably 1.1 times the permeability of air. Radial flow machine (1) according to one of the preceding claims, characterized in that the dielectric (23) is formed at least predominantly by air. Radial flow machine (1) according to one of the preceding Claims 1 - 4 , characterized in that the dielectric (23) is formed at least predominantly by polystyrene foam. Radial flow machine (1) according to one of the preceding claims, characterized in that the rotor body (22) is arranged at a distance from the rotor shaft (21) in an electrically insulated manner by at least one electrically insulating connector element (24). Radial flow machine (1) according to claim 7 , characterized in that the at least one connector element (24) is formed such that the rotor body (22) is centered coaxially to the rotor shaft (21) is held at a distance. Radial flow machine (1) according to claim 8 , characterized in that the connector element (24) is designed as an annular disk, which is supported on its radially inner end face in a circumferential direction with a sliding bearing on the rotor shaft (21) and/or on its radially outer end face in a circumferential direction with a sliding bearing against the rotor body (22). . Radial flow machine (1) according to one of Claims 7 - 9 , characterized in that the at least one connector element (24) is designed in such a way that a torque can be transmitted between the rotor body (22) and the rotor shaft (21).

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