INTERFERENCE SUPPRESSION FILTER FOR A DC MOTOR AND DC MOTOR HAVING SAID FILTER

Abstract

The present invention relates to an interference suppression filter for a DC motor (2), comprising two inductors (11, 12) each arranged in a supply line (31, 32) and a Cx capacitor (13) arranged between the supply lines (31, 32) as well as a Cy capacitor (14) arranged between one of the two supply lines (31, 32) and earth (M), wherein the impedances of the inductors (11, 12), of the Cx capacitor (13) and/or of the Cy capacitor (14) are dimensioned in such a manner that a high-frequency interference current which flows in the other of the two supply lines flows away via the Cx capacitor (13) and the Cy capacitor (14). The present invention also relates to a DC motor having the interference suppression filter.

Claims

1. An interference suppression filter (1) for a DC motor (2), comprising two inductors (11, 12) each arranged in a supply line (31, 32) and a Cx capacitor (13) arranged between the supply lines (31, 32) as well as a Cy capacitor (14) arranged between one of the two supply lines (31) and earth (M), characterized in that the impedances of the inductors (11, 12) of the Cx capacitor (13) and the Cy capacitor (14) cause a high-frequency interference current (S2) which flows in the other of the two supply lines (32) to flow away via the Cx capacitor (13) and the Cy capacitor (14) to earth (M).

2. The interference suppression filter (1) according to claim 1, characterized in that the impedances of the two inductors are the same.

3. The interference suppression filter (1) according to claim 1, characterized in that a total impedance (Z.sub.Cx+Z.sub.Cy1) of the capacitors (13, 14) of the interference suppression filter (1) is less than the impedance (Z.sub.L) of the inductors (11, 12).

4. The interference suppression filter (1) according to claim 1, characterized in that an inductive component (L.sub.Cx) of an impedance (Z.sub.Cx) of the Cx capacitor (13) for the high-frequency interference current (S2) flowing in the other of the two supply lines (32) is smaller than an inductive component (L.sub.Cy1) of an impedance (Z.sub.Cy1) of the Cy capacitor (14).

5. The interference suppression filter (1) for a DC motor (2), which comprises two inductors (11, 12) having the same impedance (Z.sub.L) and each arranged in a supply line (31, 32) and a Cx capacitor (13) arranged between the supply lines (31, 32) as well as a Cy capacitor (14) arranged between one of the two supply lines (31) and earth (M), characterized in that the impedance (Z.sub.L) of the inductors (11, 12) is greater than a total impedance (Z.sub.Cx+Z.sub.Cy1) of the Cx capacitor (13) and the Cy capacitor (14), wherein an inductive component (L.sub.Cx) of the impedance (Z.sub.Cx) of the Cx capacitor (13) for a high-frequency interference current (S2) flowing in the other of the two supply lines (32) is smaller than or equal to an inductive component (L.sub.Cy1) of an impedance (Z.sub.Cy1) of the Cy capacitor (14); thus enabling the high-frequency interference current (S2) to flow away via the Cx capacitor (13) and the Cy capacitor (14) to earth (M).

6. The interference suppression filter (1) according to claim 1, characterized in that the inductive component (L.sub.Cx) of the impedance (Z.sub.Cx) of the Cx capacitor (13) and the inductive component (L.sub.Cx) of the impedance (Z.sub.Cy1) of the Cy capacitor (14) for a high-frequency interference current (S2) flowing in the other of the two supply lines (32) is smaller than the inductive component (L.sub.L) of the impedance (Z.sub.L) of the inductors (11, 12).

7. The interference suppression filter (1) according to claim 1, characterized in that an inductive component (L.sub.Cx+L.sub.Cy1) of the total impedance (Z.sub.Cx+Z.sub.Cy1) of the capacitors (13, 14) of the interference suppression filter (1) for a high-frequency interference current (S2) flowing in the other of the two supply lines (32) is smaller than an inductive component (L.sub.L) of the impedance (Z.sub.L) of the inductors (11, 12).

8. The interference suppression filter (1) according to claim 1, characterized in that the Cx capacitor and the Cy capacitor and the inductors are wired components.

9. The interference suppression filter (1) according to claim 1, characterized in that the first supply line (31) is connected to a positive pole (+) of a DC voltage source, wherein the second supply line (32) is connected to a negative pole () of the DC voltage source.

10. ADC motor (2) comprising an interference suppression filter (1) according to claim 1.

11. The DC motor (2) according to claim 10, characterized in that the interference suppression filter (1) is disposed in the region of the brush holder.

12. The interference suppression filter (1) according to claim 1, characterized in that the inductive component (L.sub.Cx) of the impedance (Z.sub.Cx) of the Cx capacitor (13) for a high-frequency interference current (S2) flowing in the other of the two supply lines (32) is smaller than the inductive component (L.sub.L) of the impedance (Z.sub.L) of the inductors (11, 12).

13. The interference suppression filter (1) according to claim 1, characterized in that the inductive component (L.sub.Cy1) of the impedance (Z.sub.Cy1) of the Cy capacitor (14) for a high-frequency interference current (S2) flowing in the other of the two supply lines (32) is smaller than the inductive component (L.sub.L) of the impedance (Z.sub.L) of the inductors (11, 12).

14. The interference suppression filter (1) according to claim 1, characterized in that the Cx capacitor and the Cy capacitor are wired components.

15. The interference suppression filter (1) according to claim 1, characterized in that the inductors are wired components.

16. The interference suppression filter (1) according to claim 1, characterized in that the first supply line (31) is either connected to a negative pole () of a DC voltage source, wherein the second supply line (32) is connected to a positive pole (+) of the DC voltage source.

17. (negative pole ()) The DC motor (2) according to claim 10, wherein the DC motor (2) is for a motor vehicle.

18. The DC motor (2) according to claim 10, characterized in that the interference suppression filter (1) is disposed on the brush holder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the following, the invention is described by means of the drawings. The figures in the drawings are only provided by way of example and do not limit the general inventive concept. In the drawings:

[0033] FIG. 1 shows a DC motor comprising a conventional interference suppression filter which is provided for the completed interference suppression of interference emissions;

[0034] FIG. 2a shows a DC motor comprising a first embodiment of an interference suppression filter;

[0035] FIG. 2b shows the DC motor comprising a second embodiment of the interference suppression filter; and

[0036] FIG. 3 shows by way of example frequency responses of an interference emission of a common-mode interference with different interference suppression filters.

DETAILED DESCRIPTION

[0037] FIG. 1 shows the conventional interference suppression filter which has already been described above.

[0038] A first interference current S1 of a differential-mode interference is schematically delineated in the circuit. The first interference current S1 flows away via the path of the lowest impedance. Because the Cx capacitor 13 for high frequencies constitutes a short circuit, the first interference current S1 of the common-mode interference flows from the DC motor 2 across the inductor 11 arranged in the first supply line 31, across the Cx capacitor, across the inductor 12 arranged in the second supply line 32 and back to the DC motor. The inductors have an identical impedance in the circuit shown here.

[0039] A second interference current S2 of a common-mode interference flowing in the first supply line 31 flows from away the DC motor 2 via the first inductor 11 disposed in the first supply line 31 and via the first Cy capacitor 14 to earth M.

[0040] A third interference current S3 of a common-mode interference flowing in the second supply line 32 flows away from the DC motor 2 via the second inductor 12 disposed in the second supply line 32 and via the second Cy capacitor 15 to earth M.

[0041] FIG. 2 shows in (a) a DC motor 2 comprising a first embodiment of an interference suppression filter 1 according to the invention. In this embodiment, the second Cy capacitor 15 connected to the second supply line 32 is omitted. The one supply line 31, to which the one Cy capacitor 14 of the inventive interference suppression filter 1 is connected, is then here the POSITIVE line of a DC voltage source (not depicted). The interference current flowing in the other of the two supply lines 32 is subsequently denoted here as the third interference current S3. The interference suppression filter 1 otherwise corresponds to that of FIG. 1.

[0042] It can be seen that the third interference current S3 flowing across the second supply line 32, which is the NEGATIVE supply line, flows here in a third current path, which leads from the second supply line 32 via the Cx capacitor 13 to the first supply line 31 and from there via the first Cy capacitor 14 to earth M. The third interference current S3 therefore flows away from the second supply line 32 via said third current path to mass M.

[0043] In the case of the DC motor 2 comprising the second embodiment of the inventive interference suppression filter 1 of FIG. 2 (b), the first Cy capacitor 14 connected to the first supply line 31 is omitted. The one supply line 31, to which the one Cy capacitor 15 of the interference suppression filter 1 according to the invention is connected, is thus here the NEGATIVE line of the DC voltage source. The interference current flowing in the other of the two supply lines 31 is denoted below as the second interference current S2. The interference suppression filter 1 otherwise corresponds to that of FIG. 1.

[0044] It can be seen that the second interference current S2 flowing across the first supply line 31, which is the POSITIVE supply line, flows here in a second current path, which leads from the first supply line 31 via the Cx capacitor 13 to the second supply line 32 and from there via the second Cy capacitor 15 to earth M. The second interference current S2 therefore flows from the first supply line 31 via said second current path to earth M.

[0045] In order that the second interference current S2 of the interference filter 1 of FIG. 2 (b) or the third interference current S3 of the interference filter 1 of FIG. 2 (a) flows away via the Cx capacitor 13 and the one Cy capacitor 14, 15 to earth, the total impedance Z.sub.Cx+Z.sub.Cy1 of these capacitors 13, 14 of the interference suppression filter 1 is selected small with respect to the impedance Z.sub.L of the inductors 11, 12.

[0046] In addition, the Cx capacitor 13 and the Cy capacitor 14 (FIG. 2(a)), 15 (FIG. 2(b)) are dimensioned in such a manner that an inductive component L.sub.Cx of the impedance Z.sub.Cx of the Cx capacitor 13 for a high-frequency interference current S2, S3 flowing in the other of the two supply lines 32 (FIG. 2(a)), 31 (FIG. 2(b)) is smaller than or equal to an inductive component L.sub.Cy1 of an impedance Z.sub.Cy1 of the Cy capacitor 14, 15. The inductive component L.sub.Cx of the impedance Z.sub.Cx of of the Cx capacitor 13 is preferably selected smaller or even substantially smaller than the inductive component L.sub.Cy1 of an impedance Z.sub.Cy1 of the Cy capacitor 14, 15.

[0047] The Cx capacitor 13 and the Cy capacitor 14 (FIG. 2(a)), 15 (FIG. 2 (b)) are furthermore preferably dimensioned in such a manner that the inductive components L.sub.Cx, L.sub.Cy thereof are small with respect to that of the inductance L.sub.L of the inductors 11, 12 for the high-frequency interference current S2, S3 flowing through the same.

[0048] In addition, parasitic inductances are reduced by shortening electrical connection lines, in particular electrical connection lines in the second current path of the interference suppression filter 1 of FIG. 2 (b) or the third current path of the interference suppression filter 1 of FIG. 2 (c). The parasitic inductances are preferably reduced in such a manner that said inductances are negligible.

[0049] As a result, a complete interference suppression in the frequency range of 150 kHz-110 MHz, in particular from 30 MHz-110 MHz, can be achieved with the inventive interference suppression filter 1 despite the omitted second Cy capacitor.

[0050] FIG. 3 shows by way of example three frequency responses D1-D3 of a line-borne interference voltage (CEVconducted emission voltage) measured according to the international norm CISPR 25 edition 3 (Comit international special des perturbations radiolectriques). This interference voltage is a measure for the attenuation of the common-mode interference and differential-mode interference for a DC motor 2.

[0051] The first frequency response D1 shows the magnitude of the interference voltage of the common-mode interference for the DC motor 2 of FIG. 1 comprising a conventional interference suppression filter 1 as a function of the frequency. The second frequency response D2 shows the magnitude of the interference voltage of the common-mode interference of a circuit which corresponds to that of FIG. 2 (a), wherein the impedances Z.sub.Cx, Z.sub.Cy1 of the Cx and the Cy capacitor 13, 14 of the circuit of this frequency response as well as the parasitic inductances are however not optimized. Finally, the third frequency response D3 shows the magnitude of the interference voltage of the common-mode interference with the inventive interference suppression filter of FIG. 2 (a), wherein the Cx capacitor 13, the Cy capacitor 14 and the line impedances of the electrical connection lines in the current paths conducting the interference current S2, S3 are optimized. The magnitudes of the interference voltage are depicted in each case in dbV with respect to the frequency f in Hz.

[0052] The impedances Z of the Cx and Cy capacitors 13-15 have a capacitive and an inductive component, so that they can be represented by the equation Z=1/jC+jL, where C is the capacitive component and L is the inductive component.

[0053] The conventional interference suppression filter 1 (see FIG. 1), with which the first frequency response D1 was measured, comprises inductors 11, 12 having an impedance Z.sub.L, the inductance of which is L.sub.L 1.5 H. The impedance Z.sub.Cx of the Cx capacitor 13 has a capacitive component C.sub.Cx of 2.2 F and an inductive component L.sub.Cx of 6 nH; and the two Cy capacitors 14, 15 have an impedance Z.sub.Cy comprising a capacitive component C.sub.Cy of 10 nF and an inductive component L.sub.Cy of 6 nH.

[0054] In the case of the interference suppression filter 1, with which the second frequency response D2 was measured, the inductors 11, 12 have an impedance Z.sub.L, the inductance of which L.sub.L is 1.5 H. The impedance Z.sub.Cx of the Cx capacitor 13 has a capacitive component C.sub.Cx of 2.2 F and an inductive component L.sub.Cx of 6 nH; and the remaining Cy capacitor 14 has an impedance Z.sub.Cy1 comprising a capacitive component C.sub.Cy1 of 10 nF and an inductive component L.sub.Cy1 of 6 nH. Despite the omitted Cy capacitor, this second frequency response D2 shows an approximation of the first frequency response D1 up to approximately 4 MHz. From approximately 10 MHz, in particular from 30 MHz, the difference between the interference voltages U (D1), U (D2) is however more than 10 dB and is therefore insufficient.

[0055] In the case of the inventive interference suppression filter 1, with which the third, further optimized frequency response D3 was measured, the inductors 11, 12 have an impedance Z.sub.L, the inductance L.sub.L of which is 1.5 H. The impedance Z.sub.Cx of the Cx capacitor 13 has a capacitive component C.sub.Cx of 2.2 F and an optimized inductive component L.sub.Cx of 2 nH; and the remaining Cy capacitor 14 has an impedance Z.sub.Cy1 comprising a capacitive component C.sub.Cy1 of 10 nF and an inductive component L.sub.Cy1 of 2 nH. In the present exemplary embodiment, the inductive components L.sub.Cx, L.sub.Cy1 of the impedances Z.sub.Cx, Z.sub.Cy1 of the Cy capacitors 13, 14 are therefore optimized.

[0056] It is apparent that, by further optimizing the impedances Z.sub.Cx, Z.sub.Cy1 of the Cx capacitor and/or of the Cy capacitor 14 of the inventive interference suppression filter 1, a very good approximation of the attenuation of the interference emission of the common-mode interference that can be achieved by a conventional complete interference suppression is possible with said interference suppression filter 1, particularly in a frequency range greater than 30 MHz.