WO2009000290A1

WO2009000290A1 - A device for noise suppression of a small electric motor

Info

Publication number: WO2009000290A1
Application number: PCT/EP2007/005586
Authority: WO
Inventors: Jochen Langguth; Katrin Langguth; Andreas Wilk; Valerij Korsuchin
Original assignee: Sintertechnik Gmbh
Priority date: 2007-06-25
Filing date: 2007-06-25
Publication date: 2008-12-31
Also published as: EP2171832A1; EP2171832B1; ATE504971T1; DE602007013818D1

Abstract

The invention concerns a device for noise suppression of a small electric motor comprising a disk-shaped element (1) in which at least one Cx capacitor and several Cy capacitors are combined. In order to improve the noise suppression according to the invention there is provided that a first coil (10) having a predetermined inductivity is connected with its first connector (11) with a first electrode (2) of the Cx capacitor and wherein a second connector (12) thereof is provided to be connected with a first brush, wherein the first coil (10) is wound around a first section of the disk-shaped element (1).

Description

A DEVICE FOR NOISE SUPPRESSION OF A SMALL ELECTRIC MOTOR

The inventions relates to a device in accordance with the preamble of claim 1.

Such a device is known from U.S. Patent 7,019,425 B2. According to the disclosure of the aforementioned document there is provided a bar core inductivity being installed between each of the first electrodes of a C_x capacitor and a connection clamp which is provided to be connected with a power source. By the known device there can be achieved a good electromagnetic noise suppression or noise suppression, respectively, for a small electric motor. Such electric motors may be in particular part of actuators used in vehicles, aircraft and the like. However, tightened up regulations regarding the maximum tolerable noise make it necessary to further improve the noise suppression of small electric motors. At the same time there exists a need to further miniaturize electric motors and to further reduce costs.

It is an object of the present invention to overcome disadvantages in the art. It is a further object of the invention to provide a device allowing an improved noise suppression of electric motors. A further aim of the invention is to provide a device for a noise suppression which allows a further miniaturization of an electric motor and a cost reduction.

This object is solved by the features of claim 1. Embodiments of the inventions are described by the features of claims 2 to 17.

According to the invention it is provided that a first coil having a predetermined inductivity is connected with its first connector with a first electrode of the C_x capacitor and wherein a second connector thereof is provided to be con- nected with a first brush, and wherein the first coil is wound around a first section of the disk-shaped element.

According to a feature of the invention the coil of the pro- posed inductivity is wound around a first section of the disk-shaped element. By this measure there can be provided a device for noise suppression which is compact and allows the production of further miniaturized electric motors. In accordance with the present invention the disk- shaped element is used to take up the first coil. Thereby one can save mounting space and costs for providing a separate core for taking up the coil . As according to the proposed invention there is provided just one inductivity the improved noise suppression can only be achieved if the electric motor is operated always in the same sense of rotation.

According to an embodiment of the invention a second coil having the predetermined inductivity is connected with its third connector with a second electrode of the C_x capacitor and wherein a fourth connector thereof is provided to be connected with a second brush, wherein the second coil is wound around a second section of the disk-shaped element, and wherein between the first and the second sections there is provided a third section separating the coils from each other. By the proposed embodiment there is achieved an improved noise suppression even if the electric motor is operated in both senses of rotation. In this case the disk-shaped elements act as a carrier or a core for both coils.

When using the disk-shaped element as a core for taking up the coil a large core diameter can easily be realized. With an increasing core diameter the inductivity increases. Because of that the quality of the inductivity to act as a choke can be enhanced remarkably. In order to achieve an ex- cellent noise suppression there is provided a third section separating the coils from each other. By this measure unwanted interactions between the first and the second coil can be avoided. The first and the second electrodes may be covered at least partly by the first and the second coils. Thereby a compact arrangement can be achieved in which the coils are located close to the first and second electrodes of the C_x capacitor.

The first and/or the second coils may be fixed at the surface of the disk-shaped element by an adhesive. The adhesive may be made from a polymer or the like. The proposed fixing of the coils by an adhesive counteracts damages.

According to a further embodiment of the invention it is pro- vided that the first and the second coils are arranged symmetrically. This facilitates the manufacture of the device. Further, a combination with other elements of a small electric motor is enhanced.

The disk-shaped element may be designed as a ceramic multilayer element. A suitable disk-shaped ceramic multi-layer element is for example described in U.S. Patent 7,019,925 B2. The disclosure regarding the disk-shaped ceramic multi-layer element contained therein is herewith incorporated by refer- ence .

According to an alternative embodiment the disk-shaped element may also be designed as a ceramic barrier-layer element. A suitable disk-shaped ceramic barrier-layer element is for example described in U.S. Patent 7,019,425 B2. The disclosure regarding the design of a disk-shaped ceramic barrier-layer element described therein is incorporated herewith by reference . According to a further advantageous feature a first isolation path electrically separates the first and the second electrodes, and second isolation paths electrically separate the third electrode from the first and the second electrodes. The first and the second isolation paths may have the form of a "Y" or the like. The proposed design of the electrodes and the isolation paths allows for the integration of a C_x capacitor with a high capacity with C_y capacitors within one disk.

According to a further embodiment a first discrete capacitor being mounted on the disk-shaped element is switched between the first and the second electrodes. I.e. the first discrete capacitor is connected in parallel with the C_x capacitor. In a similar way a second discrete capacitor being mounted on the disk-shaped element may be switched between the third electrode and at least one of the first and second electrodes. Although, the second discrete capacitor is connected in parallel with the C_y capacitor. By the proposed features the capacity of the C_x and/or the C₇ capacitors can be increased. Therewith, in dependence of the noise characteristic of the electric motor the noise can be suppressed effectively. The first and/or second discrete capacitor/s is/are SMD element/s. Such elements are available commercially at a low price. A mounting of such elements on the surface of the disk-shaped element is easy. The coefficients of expansion of the discrete capacitor, e.g. multilayer capacitor, and the disk-shaped element are very similar so that a damage of the discrete capacitors due to thermal effects is highly un- likely.

According to a further embodiment the first electrodes are connected with a resistor having a resistance in the range of 10 Ω to 100 kΩ. The provision of proposed resistor enhances the protection against a high voltage breakthrough through the dielectric layers.

Furthermore, the first and the second electrodes may be con- nected with a NTC-resistor or a VDR-device. Such elements may be produced by printing techniques, e.g. screen-printing. By providing the proposed resistor and/or other elements in particular current peaks can be compensated and the durability of the proposed device can be enhanced.

The disk-shaped element may have a central breakthrough for feeding through a shaft. This makes it possible to combine the proposed device with conventional electric motors. In particular the proposed device may be combined with an end cap of a small electric motor. In this connection it has turned out to be advantageous that the disk-shaped element covers an inner end face of the end cap. Advantageously, the disk-shaped element fully covers the inner end face. Thereby, the end cap shields against an escape of electromagnetic noise from the interior of a housing surrounding the electric motor.

According to a further aspect of the invention there is provided a small electric motor, comprising a housing which is closed with the aforementioned end cap.

Preferred embodiments are know described by reference to the enclosed figures.

Fig. 1 shows a plan view upon a device,

Fig. 2 shows a sectional view through an end cap,

Fig. 3 shows a perspective view of the end cap of Fig. 2, Fig. 4 shows plots of conducted emissions in dependency of the frequency for a conventional electric motor and an electric motor provided with a device according to the invention,

Fig. 5 shows plots of radiated emissions in dependency of the frequency for a conventional electric motor and an electric motor provided with a device according to the invention and

Fig. 6 shows a substitute circuit diagram.

Fig. 1 shows a plan view upon a device of the invention. A disk-shaped element 1 has a more or less rectangular circum- ference with rounded corners. The disk-shaped element 1 is preferably a multi-layer element or a barrier-layer capacitor in which C_x and C_y capacitors are combined. Moreover the disk-shaped elements 1 may be further comprise feedthrough capacitors C₀. As dielectric materials for the manufacture of the disk-shaped element 1 there can be used materials which are effective up to frequencies of 50 GHz. Suitable dielectric materials are for example materials with HDK and/or NDK properties such as for example dielectric materials like X7R, Y5V, NPO, COG as well as microwave ceramics, barium titanate, strontium titanate, calcium titanate or mixtures thereof.

Besides that the C_x and C_y capacitors can be barrier-layer capacitors being integrated within one disk. In this case, the disk-shaped element 1 may be made from a perowskite mate- rial, e.g. a mixed titanate, for example strontium titanate, barium titanate, calcium titanate or suitable mixtures thereof having a VDR characteristic. On an upper side of the disk- shaped element 1 there is provided a first electrode 2 and a second electrode 3 of a C_x capacitor. Reference sign 4 designs a third electrode of a C_y capacitor. The first 2 and the second electrode 3 are separated by a first isolation path 5 as well as by second isolation paths 6. The second isolation paths 6 separate at the same time the first 2 and the second electrode 3 from the third electrode 4. The elec- trodes 2, 3, 4 are preferably made from a layer of silver, copper or the like. Such a layer may be manufactured by printing techniques.

In order to increase or adjust the capacity of the C_x capaci- tor the first isolation path 5 may be bridged by a first SMD capacitor 7. In order to increase the capacity of the C_y capacitor in a similar way the second isolation path 6 may be bridged by second SMD capacitors 8. From the electric view point the first SMD 7 and the second SMD capacitors 8 are switched in parallel with respect to the C_x capacitor and the C_y capacitor, respectively. Reference 9 designates a central breakthrough being provided within the disk-shaped element 1. A diameter of the central breakthrough 9 is adjusted such that a shaft of the small electric motor can be conducted through it so that the shaft can freely rotate.

In a first section of the disk-shaped element 1 which is covered by the first electrode 2 there is provided a first coil 10. The first coil 10 is wound around the disk-shaped element 1. The first coil 10 is made of a wire the first end of which forms a first connector 11 which is electrically connected with the first electrode 2. A second end of the wire forms a second connector 12 which is provided to be connected with a first brush (not shown here) of the small electric motor.

Similar to the first coil 10 there is provided a second coil 13 being wound around the disk-shaped element 1 in a second section which is covered by the second electrode 3. A third connector 14 of the second coil 13 is electrically connected with the second electrode 3. A fourth connector 15 of the second coil 13 is provided to be connected with a second brush (not shown here) of the small electric motor. The first 11 and the third connector 14 may be electrically connected with the first 2 and the second electrode 3 by conventional methods, like soldering, welding or glueing with electric conductive clue.

Besides that there may be provided a first terminal extending from the first electrode 2 and/or a second terminal extending from the second electrode 3. Such terminal/s may be in the form of a pin or the like which is mounted with electric contact on the first 2 and/or second electrode 3. The provision of such terminal/s makes it not only possible to contact the first 12 and/or third connector 14 with the first 2 or second electrode 3, respectively, but also to connect connecting wires of a power source with the first 2 and/or second electrode 3.

Fig. 2 shows a sectional view through an end cap 16 of a small electric motor. The end cap 16 may be made of a polymer. It may be manufactured for example by injection molding. A shaft 17 is conducted through the central breakthrough 9 of the disk-shaped element 1. An inner end face 18 of the end cap 16 is provided with recesses 19. The form of the recesses 19 corresponds to a height and a width of first 10 and second coil 13 so that the disk-shaped element 1 can be positioned with its remaining surface in direct contact on the inner end face 18. I. e. the recesses 19 form pockets for taking up a projection formed by the first 10 and second coil 13.

The disk-shaped element 13 shown in the embodiment of Fig. 2 and 3 has further recesses 20 in the circumference which are located within the first and/or second section around which the first 10 and second coil 13 are wound. Although not ex- plicitly shown in Fig. 3 it has to be understood that for each coil 10, 13 there are provided two further recesses 20 in an opposite direction. The provision of the proposed further recesses 20 facilitates the manufacture of the device, i. e. the production of a winding upon the disk-shaped element .

As can further be seen from Figs. 2 and 3 the disk-shaped element essentially covers the inner end face 18 of the end cap 16. By this measure an improved shielding vis-a-vis electromagnetic noise produced by the small electric motor can be achieved.

Figs. 4 and 5 show the results of measurements of electromag- netic emissions or noise of a conventional electric motor having a conventional noise suppressing VDR-device at the commutator and the same electric motor being provided with a device for noise suppression in accordance with the present invention. The values measured for the conventional electric motor are signified by "crosses", the values measured for the electric motor being provided with a device for a noise suppression in accordance with the present invention are signified by "dots" . The measurements have been carried out in accordance with the norm CISPR25.

As can be seen from Figs. 4 and 5 by use of the device for noise suppression in accordance with the present invention the conducted emissions (Fig. 4), i.e. emissions which are emitted via a wire, as well as the radiated emissions (Fig. 5) are suppressed remarkably.

Fig. 6 shows a substitute circuit diagram of a circuit for noise suppression of a small electric motor. A C_x capacitor is installed between connection clamps ATI, AT2 which are used for the connection to a source of current. Further, each electrode of the C_x capacitor is connected via an inductivity Ll, L2 with a first brush Bl and a second brush B2 , by which a sliding contact to commutator is realized. Parallel to the C_x capacitor, a varistor V may be installed. Instead or in addition to the varistor V an ohmic resistor can also be provided or a diode. Each of the connection clamps ALl, AL2 as well as each of the inductivities Ll, L2 are also connected via a C_y capacitor with ground. C_D designates a feedthrough capacitor which may be provided additionally.

List of reference signs

1 disk-shaped element

2 first electrode

3 second electrode

4 third electrode

5 first isolation path

6 second isolation path

7 first SMD capacitor

8 second SMD capacitor

9 central breakthrough

10 first coil

11 first connector

12 second connector

13 second coil

14 third connector

15 fourth connector

16 end cap

17 shaft

18 end face

19 recess

20 further recess

ALl first connection clamp AL2 second connection clamp

Bl first brush

B2 second brush

El first end

E2 second end Ll first inductivity

L2 second inductivity

V varistor

Claims

1. A device for noise suppression of a small electric motor, the device comprising:

a disk-shaped element (1) in which at least one C_x capacitor and several C₇ capacitors are combined,

characterized in that

a first coil (10) having a predetermined inductivity is connected with its first connector (11) with a first electrode (2) of the C_x capacitor and wherein a second connector (12) thereof is provided to be connected with a first brush, and wherein the first coil (10) is wound around a first section of the disk-shaped element (1) .

2. The device of claim 1, wherein a second coil (13) having the predetermined inductivity is connected with its third connector (14) with a second electrode (3) of the C_x capacitor and wherein a fourth connector (15) thereof is provided to be connected with a second brush, wherein the second coil (13) is wound around a second section of the disk-shaped element (1) ,

and wherein between the first and the second sections there is provided a third section separating the coils (10, 13) from each other.

3. The device of one of the preceding claims, wherein the first electrode (2) is at least partially covered by the first coil (10), and wherein the second electrode (3) is at least partially covered by the second coil (13) .

4. The device of one of the preceding claims, wherein the first (10) and/or the second coils (13) are fixed at the surface of the disk- shaped element (1) by an adhesive.

5. The device of one of the preceding claims, wherein the first (10) and the second coils (13) are arranged symmetrically.

6. The device of one of the preceding claims, wherein the disk-shaped element (1) is designed as a ceramic multi-layer element .

7. The device of one of the preceding claims, wherein the disk-shaped element (1) is designed as a ceramic barrier- layer element.

8. The device of one of the preceding claims, wherein a first isolation path (5) electrically separates the first (2) and the second electrodes (3), and second isolation paths (6) electrically separate a third electrode (4) of the C_y capacitor from the first (2) and second electrodes (3) .

9. The device of one of the preceding claims, wherein a first discrete capacitor (7) being mounted on the disk-shaped ele- ment (1) is switched between the first and the second electrodes .

10. The device of one of the preceding claims, wherein a second discrete capacitor (8) being mounted on the disk- shaped element (1) is switched between the third electrode (4) and at least one of the first (2) and second electrodes (3) .

11. The device of one of the preceding claims, wherein the first (7) and/or second discrete capacitor (8) is a SMD element .

12. The device of one of the preceding claims, wherein the first (2) and second electrodes (3) are connected with a resistor having a resistance in the range of 10 Ω to 100 kΩ.

13. The device of one of the preceding claims, wherein the first (2) and the second electrodes (3) are connected with a

NTC-resistor or a VDR-device or a diode.

14. The device of one of the preceding claims, wherein the disk-shaped element (1) has a central breakthrough (9) for feeding through a shaft (17) .

15. An end cap (16) for a small electric motor in which there is mounted an device according to one of the previous claims .

16. The end cap (16) of claim, wherein the disk-shaped element (1) essentially covers an inner end face (18) of the end cap (16) .

17. A small electric motor, comprising a housing which is closed with the end cap (16) according to one of claims 14 or 15.