WO2015185261A1

WO2015185261A1 - Electric machine having a rotary-disk capacitor for conducting away hf disturbing currents

Info

Publication number: WO2015185261A1
Application number: PCT/EP2015/058688
Authority: WO
Inventors: Dennis BURGER; Shinichiro Nishizawa
Original assignee: Robert Bosch Gmbh
Priority date: 2014-06-04
Filing date: 2015-04-22
Publication date: 2015-12-10
Also published as: DE102014210538A1

Abstract

The invention relates to an electric machine, wherein high-frequency disturbing currents, which can occur, for example, in the case of control by means of a pulse-width-modulated inverter, are advantageously conducted away. The electric machine (1) comprises a stator (3), a rotor (5), a rotor shaft (7), and a housing (9). A disk (21) composed of an electrically conductive material is arranged on the rotor shaft (7) in a region (19) protruding beyond the rotor (5). Said disk is dimensioned in such a way and arranged near a surface (23) of the housing (9) facing the disk in such a way that high-frequency disturbing electric currents can be transmitted via a gap (25) between the disk (21) and the housing (9) similarly to the case of a rotary-disk capacitor. Disturbing currents in a frequency range of 10 kHz to 30 MHz can be conducted away without friction and thus without wear in this way.

Description

description

Electric machine with turntable condenser for the discharge of HF interference currents

Field of the invention

The present invention relates to an electrical machine, in particular an example, pulse inverter-driven electric machine in which high-frequency (RF) interference currents occur in a rotor.

State of the art

Electric machines are used as motors or generators for a variety of purposes. For example, electric machines are used in electric or hybrid vehicles as a motor for driving or as a generator for Rekuperieren kinetic energy. Electric machines are also used for other, especially industrial purposes.

Electrical machines are usually powered by an inverter. Especially when using pulse inverters can steep

Voltage edges (nanosecond range) occur and induce high-frequency interference currents within a rotor of the electrical machine. The interference currents can typically occur in a frequency range of 10 kHz to 20 MHz. Such interference currents will flow outside the electrical machine and may interfere with adjacent electrical or electronic systems. These interference currents (common mode) should therefore be derived from the rotor, for example, to the electric machine housing serving as the electrical ground.

To dissipate interference currents within an electrical machine from the rotor to the housing, conventionally, for example, highly conductive ball bearings or multiple carbon brushes or carbon fibers are used. However, especially in electrical machines that are in the

Automotive sector are to be used and should therefore be operated within a wide temperature range of, for example, -40 ° C to +120 ° C, problems arise in that a lubricating effect of the grease used in the highly conductive ball bearing can subside and it can lead to bearing damage, for example , When using multiple carbon brushes can result in an unavoidable wear and thus necessary replacement of the carbon brushes considerable costs. When using carbon fibers to dissipate the RF interference currents, it has been observed that a parasitic effect can decrease at high frequencies above 500 kHz.

Disclosure of the invention

With embodiments of the present invention is an electrical

Machine proposed in which advantageously high-frequency

Interference currents, which may occur within the rotor, can be dissipated to the surrounding housing. The interference currents can thereby

be advantageously derived such that the electric machine can be operated within a wide temperature range, a

Storage of the rotor is substantially unaffected, a derivative of the interference currents substantially non-contact and thus can be carried out wear-free and / or interference currents within a large frequency range can be derived up to, for example, 30 MHz.

According to one aspect of the invention, an electric machine

proposed, which has a stator, a rotor, a rotor shaft and a housing. The housing surrounds the stator and the rotor. The rotor is rotatable relative to the stator. In the center of the rotor is the

Rotor shaft around which the rotor can rotate. The electrical machine is characterized in that a disc made of an electrically conductive material is arranged on the rotor shaft in a region projecting beyond the rotor. The disc is dimensioned in this case and arranged so close to an opposite surface of the housing, that via a

Gap between the disc and the housing high-frequency electrical Interference currents that occur within the rotor can be transferred capacitively.

Ideas for embodiments of the proposed electric machine may be considered, inter alia, as being based on the thoughts and findings described below:

It has been recognized that the conventional ones described in the introduction

Measures for deriving high-frequency interference currents in an electrical machine can be associated with different disadvantages. These conventional approaches have in common that an electrical discharge of the interference currents is achieved via a mechanical contact between parts of the rotor and parts of the surrounding housing. However, such a mechanical contact can lead to wear and / or disadvantages in the storage of the rotor, for example due to unavoidable friction occurring.

It was therefore sought after a way to derive interference currents from the rotor friction or preferably without contact to the surrounding housing.

Since the interference currents in electrical machines typically have high frequencies above 10 kHz, in particular they can also be transmitted capacitively. In order to enable a sufficient capacitive derivative of the interference currents from the rotor, it is proposed to provide an additional disk on the rotor shaft in a region projecting beyond the rotor. The rotor disk is held on the rotor shaft or coupled therewith, so that it can rotate with the rotor during operation of the electric machine. This disk can form part of a capacitor, by means of which the electrical currents transmitted to the rotor via the rotor shaft can be capacitively transmitted to the adjacent housing. The disc and the opposite surface of the housing can act much like a plate capacitor. The interference currents occurring in the rotor can lead to a temporary shift of electrical charges towards the disk or out of the disk, charges accumulated in the disk due to the small distance between them the disc and the opposite surface of the housing in the

Housing in turn can lead to a charge shift, so that it can effectively come across the lying between the disc and the housing gap across a high-frequency electric current. Since the disc arranged on the rotor shaft can rotate together with the rotor during the operation of the electric machine, in this context it is also referred to as a rotary disc capacitor.

In order to be able to sufficiently dissipate interference currents from the rotor, it can be particularly advantageous to dimension the disk in such a way and to arrange it close to an opposite surface of the housing and a medium within the gap between the disk and the disk

opposite housing surface to be selected such that with the disc and the opposite surface of the housing, a capacitor having a capacity of at least 1 nF, preferably at least 5 nF, is formed.

In other words, parameters that affect the capacitance of the variable capacitor formed between the disc and the housing may be suitably selected so that the variable capacitor has a capacitance of at least 1 nF, preferably at least 5 nF.

These parameters include, but are not limited to, the size of the surface of the disk facing a corresponding surface of the housing with only a small gap therebetween. Like one

Plate capacitor takes the capacity of the thus formed

Rotary disc condenser with the surface of the disc too. For example, it may be advantageous to choose the pane such that its

Cross-sectional area is greater than the cross-sectional area of the rotor shaft. When of a circular disc and a cylindrical rotor shaft

is assumed, this means that the diameter of the disc can be greater than the diameter of the rotor shaft. In particular, the

Diameter of the disc be greater than half the diameter of the rotor.

In a particular embodiment, the disc may be with two or more

Teilscheiben be configured, which together form a total disc, to achieve higher capacity values. In other words, instead of a single large disk, two or more small disks may be used to form the turntable condenser. As a further, the capacity of the variable capacitor influencing parameters, the width of the gap formed between the disc and the opposite surface of the housing can be suitably selected. In general, as the width of the gap becomes smaller, the capacity of the gap increases

Rotary capacitor increases. Suitable high capacities for sufficient dissipation of interference currents can be obtained if the width of the gap is less than 4 mm, preferably less than 2 mm, and more preferably less than 1 mm. For example, but not to have to comply with very accurate tolerances or run the risk that the disc during operation of the electric machine, for example, when vibrations or shaking on the opposite surface of the housing grind, the gap should not be less than 0.1 mm, preferably not smaller than 0.3 mm.

Furthermore, the capacity of the variable capacitor is also influenced by the medium, that is, the material which is located within the gap between the disc and the opposite housing surface. in the

Contrary to the materials of the disc and the housing, which are to be electrically conductive and to be made of metal, for example, an electrically insulating material must be arranged within the gap. For example, within the gap, a layer of a dielectric

Material arranged. The dielectric material may be a solid material. In particular, the dielectric material may have a permittivity that is substantially greater than the permittivity of gases, especially air.

Alternatively, a liquid dielectric material may be disposed within the gap. For example, a water-based dielectric can be used. By using a liquid dielectric material, on the one hand, the gap may preferably be completely filled with dielectric material, thus maximizing a capacity of the variable capacitor, on the other hand, friction losses may occur between the capacitor rotating disk and the stationary housing wall are minimized. Such a liquid dielectric material may be, for example, a water-based cooling medium of the electric machine or, alternatively, also, for example, windscreen wiper water in a motor vehicle. One

Water-based dielectric can typically have a very high relative

Dielectric constant of between 50 and 100 have.

In order to be able to cube liquid dielectric material in the electrical machine and thus within the gap, for example around one

To be able to cause sufficient cooling of the same, may be provided in the housing of the electric machine, an inlet and an outlet for supplying and discharging the liquid dielectric material. Further, suitable seals may be provided between the shaft and the housing.

Sufficiently high capacitance values for the rotating disk capacitor can be achieved, for example, with dielectric materials which have a high capacitance

Permittivitätszahl, which partly as relative permittivity or

Dielectric constant is greater than 5, preferably more than 25, have.

For example, the dielectric material may be a ceramic material or a polymeric material, which typically has permittivity numbers in the range 5 to 10. The dielectric material may also be diamond, ruby,

Germanium or the like, which typically have permittivity numbers in the range of 10 to 20. Advantageously, the dielectric material may also be provided as paper impregnated with glycerol (eg, structural formula C ₃ H ₈ 0 ₃ ), which typically has a permittivity number of about 30 and may entail the advantage of low cost. Alternatively, the dielectric material may also be provided as oxidized metal, which may typically have permittivity numbers in the range of 30 to 60.

The layer of dielectric material may substantially, for example, more than 50% or more than 80%, but preferably not complete, ie less than 99% or less than 95% of the gap between the disc and the opposite surface of the housing. fill out. With others In words, a predominant portion of the gap may be filled with the dielectric layer, but it should preferably continue to remain only with gas, in particular air, filled residual gap between the rotatable disc and the stationary surface of the housing, so that the disc during operation of the electric Machine can rotate largely frictionless.

The described embodiments of an electrical machine, between whose rotor shaft and its housing a rotary disk condenser is formed, may be particularly advantageous for electrical machines which are designed to be operated by means of a pulse-controlled inverter. Such electrical machines are often used e.g. designed as synchronous machines for use in electric or hybrid vehicles. In this case, the electric machine is operated via the modern pulse-controlled inverter with a high voltage of, for example, 200 to 600 V at a clock frequency of 10 to 30 kHz and a slope of 100 to 200 ns. The high clocked high voltage can couple to the rotor shaft and generate high frequency noise currents, which can have frequencies in the range of 10 kHz to 30 MHz.

Such interference currents can, if they are not short (low resistance) are derived against the engine housing (mass), a vehicle electronics such as electronics in a controller or a radio significantly disturb.

It should be noted that possible features and advantages of electrical machines according to the invention are described herein with reference to FIG

different embodiments of the invention are described. One

A person skilled in the art recognizes that the features can be suitably combined or replaced in order to arrive at further embodiments of the invention.

Brief description of the drawings

Hereinafter, embodiments of the invention will be described with reference to the drawings, wherein neither the description nor the

Drawings are to be construed as limiting the invention. Figure 1 shows in cross section an electric machine according to a

Embodiment of the present invention.

FIG. 2 shows a frequency behavior of interference currents within an electrical machine (rotating rotor).

FIG. 3 shows details of an electrical machine according to another

Embodiment of the present invention with liquid dielectric.

The figures are only schematic and not to scale.

DETAILED DESCRIPTION FIG. 1 shows an electrical machine 1 according to one embodiment of the invention

Invention. The electric machine 1 has a stator 3, a rotor 5, a rotor shaft 7 and a housing 9. The stator 3 is fixedly connected to the housing 9, wherein the housing 9 surrounds both the stator 3 and the rotor 5. The housing 9 is formed in two parts in the example shown with a housing pot 13 and a lid 15 which can be screwed to an end face of the electric machine 1 to the housing pot 13. The housing 9, in particular its lid 15, consist of an electrically conductive material, preferably of metal. The rotor 5 is composed of a laminated core 1 1 and magnets 32, in whose

Center is provided a recess into which the rotor shaft 7 engages, which is mounted in a ball bearing 30. At a projecting portion of the rotor shaft 7, a speed sensor 17 is arranged. With the help of this

Speed sensor, a speed or a current angular orientation of the rotor 5 is determined and used for example to control the electric machine 1.

At one end of the rotor shaft 7, a disc 21 is arranged made of an electrically conductive material. The disk 21 is formed for example as a metal, thin circular disk and is electrically galvanic with the

Rotor shaft connected, for example screwed. The disc 21 has Typically, for example, if the entire rotor 5 has a diameter of several centimeters, for example about 10 cm, the diameter of the disc 21 may be selected to be similarly large, for example in FIG range from 5 to 15 cm. The disc 21 can only do less

Millimeters, for example, between 1 mm and 20 mm thick.

The disc 21 is formed and arranged on the rotor shaft 7, that only a narrow gap 25 remains between this disc 21 and an opposite surface 23 of the lid 15 of the housing 9. This

Gap may have a width of less than 4 mm, preferably even less than 1 mm. Due to the small spacing of the disk 21 to the opposite surface 23 of the housing 9, there is a significant capacitive coupling between these two electrically conductive

Components. The arrangement of disc 21 and opposite surface

23 of the housing 9 can thus act as a turntable condenser and capacitively couple the standing with the disc 21 in electrical connection rotor shaft 7 with the housing 9, which in turn is grounded via a ground 29.

In order to further increase the capacity of the rotating disk capacitor, a layer 27 of a dielectric material may be provided within the gap 25. This layer can, for example, with a small thickness of 0.5 to 1 mm, for example, on the inside of the lid 15 of the

Housing 9, that is on the disc 21 opposite surface of the

Housing 9, be applied. Alternatively or additionally, a dielectric layer may also be formed on a surface of the disk 21 directed toward the inside of the housing. The layer 27 may be made of, for example, ceramic or of a paper impregnated with glycerin oil.

Alternatively or additionally, in the housing 9 and in particular in the region of the gap 25, a liquid dielectric material may be provided to the capacity of the disc 21 and the opposite

Case surface formed to increase rotary capacitor. The liquid dielectric material may be supplied via inlets and outlets (not shown) to and be removed and continuously replaced or circulated during operation, for example, to avoid local overheating.

In order to further increase the capacity of the rotary disk condenser, inwardly projecting projections 31 may be provided on the housing 9, in particular on the cover 15, in a region radially adjacent to the disk 21

be provided. These projections 31 may be formed as a circular ring and enclose the disc 21 annular radially outside, so that also here only a narrow gap remains. Also, this narrow gap may be at least partially filled with a dielectric material.

Depending on how large the disc 21 is, that is, how large is the area at which the disc 21 is adjacent to the opposite surface 23 of the housing 9, how wide the gap 25 is and what permittivity possibly in the gap 25th has provided dielectric material, the turntable capacitor formed thereby capacitance values of significantly more than 1 nF, preferably in the range of about 10 nF, have.

The rotor shaft 7 can be capacitively coupled to the grounded housing 9 via the turntable capacitor of sufficient capacity.

High-frequency interference currents, which are generated during operation of the electric machine 1 in the rotor 5 and transmitted to the rotor shaft 7, can thus be derived to the housing 9.

This is illustrated in the graph of FIG. The graph enters

Voltage Noise UR (English: noise voltage) as a function of the frequency v generated high frequency noise.

As can be seen from Figure 2, in the absence of capacitive coupling of the rotor 5 to the housing 9, that is at a capacity of

Turntable capacitor of 0 nF, a voltage noise U _R in the entire frequency range of 10 kHz to 30 MHz significantly higher than in a case in which a significant coupling of the rotor 5 via a

Turning disk capacitor takes place on the housing 9 and, for example, a capacity of this turntable capacitor is greater than 1 nF, preferably even greater than 5 nF. For capacities of more than 5 nF is a remaining voltage noise only slightly higher than one

Background noise level U _R0 . The electrical machine appears thus sufficiently suppressed over the entire frequency range. FIG. 3 shows details of an electrical machine 1 according to another

Embodiment. As in the embodiment described above, a disc 21 is provided on the rotor shaft 7. The disc 21 is designed in two parts in this case, i. consists of two partial discs 20, 22, which are held together by means of screw 37. Between the part discs 20, 22 is an air pocket 24. Around the disc 21 is around a

Electrode 33 is provided which is electrically connected to the housing 9 of the machine 1 to ground 39. The electrode 33 surrounds the disk 21 such that a gap 25 is formed between it and the disk 21. In the described embodiment, a dielectric of liquid material 26 is filled in this gap 25, for example a water-based dielectric. Opposite the

Rotor shaft 7, the electrode is sealed by means of seals 35 to a

To avoid leakage of the liquid dielectric.

Claims

claims

Electric machine (1), comprising:

a stator (3),

a rotor (5),

a rotor shaft (7),

a housing (9) surrounding the stator (3) and the rotor (5);

characterized in that

a disc (21) of an electrically conductive material is arranged on the rotor shaft (7) in a region (19) projecting beyond the rotor (5), the disc (21) being dimensioned in such a way and being close to an opposite surface (23 ) of the housing (9) is arranged, that over a gap (25) between the disc (21) and the housing (9) high-frequency electrical interference currents that occur within the rotor (5) can be transmitted capacitively.

Electric machine according to claim 1, wherein the disc (21) is dimensioned in such a way and is arranged so close to an opposite surface (23) of the housing (9) and a medium within the gap (25) is selected such that with the disc ( 21) and the opposite surface (23) of the housing (9) a rotary disc capacitor having a capacity of at least 1 nF, preferably at least 5 nF, is formed.

Electric machine according to claim 1 or 2, wherein in the gap (25) a layer (27) of a dielectric material is arranged.

An electric machine according to claim 1 or 2, wherein liquid dielectric material (26) is disposed in the gap (25).

The electric machine of claim 4, wherein the liquid dielectric material (26) is a water-based dielectric.

6. Electrical machine according to claim 4 or 5, wherein the gap (25) by means of seals (35) against the rotor shaft (7) is sealed.

7. Electrical machine according to claim 4, 5 or 6, wherein in the housing an inlet and an outlet for supplying and discharging the liquid dielectric

Material (26) is provided.

8. Electrical machine according to one of claims 3 to 7, wherein the

dielectric material has a permittivity number greater than 5, preferably greater than 25.

9. Electrical machine according to one of claims 1 to 8, wherein the gap (25) is smaller than 4mm, preferably smaller than 2mm. 10. Electrical machine according to one of claims 1 to 9, wherein the disc

(21) has a larger diameter than the rotor shaft (7).

1 1. Electric machine according to one of claims 1 to 10, wherein the

Disc (21) has a diameter greater than half the diameter of the rotor (5).

12. Electrical machine according to one of claims 1 to 1 1, wherein the

Disc (21) is composed of several part discs. 13. Electrical machine according to one of claims 1 to 12, wherein the

Washer (21) and / or the housing (9) consists of metal.

14. Electrical machine according to one of claims 1 to 13, wherein the

Interference currents at common mode frequencies in the range of 10 kHz to 30 MHz.

15. Electrical machine according to one of claims 1 to 14, wherein the

electrical machine (1) is designed by means of a

Pulse inverter to be operated.