BRUSH-COMMUTATED DC ELECTRIC MOTOR WITH AN IMPROVED OSCILLATION BEHAVIOR

Abstract

The DC electric motor has a stator which comprises a permanent magnet with a number p of pole pairs, and has a rotor which can rotate in relation to the stator and has a hollow-cylindrical iron-free winding with a geometric axis and a number Q of sub-coils, and a collector with a number K of collector segments, wherein the sub-coils are arranged distributed over the periphery of the rotor. The brush-commutated DC electric motor furthermore has at least one pair of brushes which are in contact with the collector and by means of which the sub-coils are energized. The arrangement of the brushes and the interconnection of the sub-coils are selected in such a way that in each case a number n≥2 of sub-coils, which are each arranged offset by 360°/n in a rotationally symmetrical manner with respect to the axis of the rotor, are always supplied with the same current at the same time.

Claims

1. A brush-commutated DC electric motor having a stator comprising a permanent magnet, having a number p of pole pairs, and having a rotor rotatable with respect to the stator, which has a hollow-cylindrical iron-free winding with a geometric axis and a number Q of sub-coils, and a collector with a number K of collector segments, wherein the sub-coils are arranged distributed over the periphery of the rotor, and wherein the brush-commutated DC electric motor furthermore has at least one pair of brushes which are in contact with the collector and by means of which the sub-coils are energized, wherein the arrangement of the brushes and the interconnection of the sub-coils are selected in such a way that in each case a number n≥2 of sub-coils, which are each arranged offset by 360°/n in a rotationally symmetrical manner with respect to the axis of the rotor, are always supplied with the same current at the same time.

2. The brush-commutated DC electric motor according to claim 1, wherein the sub-coils have a uniform shape at least in a projection onto an envelope of the hollow-cylindrical iron-free winding.

3. The brush-commutated DC electric motor according to claim 1, wherein the n sub-coils which are each arranged in a rotationally symmetrical manner with respect to each other and are always energized at the same time are connected in series.

4. The brush-commutated DC electric motor according to claim 1, wherein the n sub-coils which are each arranged in a rotationally symmetrical manner with respect to each other and are always energized at the same time are connected in parallel.

5. The brush-commutated DC electric motor according to one of claim 1, wherein the number p of pole pairs is 1, wherein the collector (10) has an uneven number K≥3 of collector segments, wherein the number Q of sub-coils is 2.Math.K, and wherein the number n of the sub-coils which are each arranged in a rotationally symmetrical manner with respect to each other and are always energized at the same time is 2.

6. The brush-commutated DC electric motor according to claim 5, wherein each sub-coil is connected to a collector segment at one end, and to the diametrically opposed sub-coil at the respective other end.

7. The brush-commutated DC electric motor according to one of claim 1, wherein the number p of pole pairs is greater 1, wherein the collector has a number K=k.Math.p of collector segments, wherein k is an uneven number ≥3, wherein the number Q of sub-coils is q.Math.p, wherein the number q either corresponds to the number k or to the double of the number k, and wherein the number n of the sub-coils which are each arranged in a rotationally symmetrical manner with respect to each other and are each energized at the same time corresponds to the number p, if q=k, or the double of p, if q=2.Math.k, wherein a number p of collector segments, which are also each arranged offset by 360°/p in a rotationally symmetrical manner with respect to the axis of the rotor, are connected to each other in a conductive manner on the rotor side.

8. The brush-commutated DC electric motor according to one of claim 1, wherein the two brushes of the pair of brushes each have a width corresponding to the sum of half a collector pitch and the distance between two collector segments, wherein the two brushes are arranged such that the beginning of the commutation process of the one brush of the pair occurs simultaneously with the termination of the commutation process of the respective other brush of the pair.

9. The brush-commutated DC electric motor according to claim 7, wherein the pair of brushes is a first pair of brushes, wherein the brush-commutated DC electric motor furthermore comprises at least one further pair of brushes which are also in contact with the collector, wherein the two brushes of the further pair of brushes each have a width that is smaller than the width of the brushes of the first pair of brushes.

10. The brush-commutated DC electric motor according to claim 9, wherein the brushes of the at least one further pair of brushes consist of a material which has a higher conductance than the materials of which the brushes of the first pair of brushes consist.

11. The brush-commutated DC electric motor according to claim 1, wherein all sub-coils have the same shapes.

12. The brush-commutated DC electric motor according to claim 1, wherein the sub-coils are designed to be chorded and/or chamfered with respect to the axis of the rotor.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0022] Embodiments of the present disclosure will be illustrated more in detail below with reference to drawings.

[0023] In the drawing:

[0024] FIG. 1 shows a schematic exploded view of a brush-commutated DC electric motor,

[0025] FIG. 2 shows a schematic representation of the sub-coil interconnection of a two-pole brush-commutated DC electric motor according to a first embodiment of the present disclosure,

[0026] FIG. 3 shows the representation of FIG. 2 with additionally represented brushes,

[0027] FIG. 4 shows an unwinding of the hollow-cylindrical iron-free winding of the embodiment of FIGS. 2 and 3 with a representation of the winding geometry and the associated interconnection of the individual sub-coils,

[0028] FIG. 5 shows a schematic representation of the sub-coil interconnection of a four-pole brush-commutated DC electric motor according to a second embodiment of the present disclosure, and

[0029] FIG. 6 shows a schematic representation of the sub-coil interconnection of a four-pole brush-commutated DC electric motor according to a third embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

[0030] In the following illustrations, equal parts are designated by equal reference numerals. If a figure contains reference numerals which are not discussed in greater detail in the pertaining description of the figures, reference is made to preceding or following descriptions of the figures.

[0031] With respect to FIG. 1, first of all, the general structure of a brush-commutated DC electric motor 4 is illustrated. The substantial components of a DC electric motor 4 with an iron-free winding are the stator 5 and the rotor 7 rotatably mounted with respect to the stator. The stator 5 includes, as substantial components, a permanent magnet 6 which can be of a hollow-cylindrical design, a flange 13 positioning the permanent magnet 6, a magnetic return 16 consisting of iron and serving as a housing, and a further flange 14 which serves as a brush or housing cover and to which two collector brushes 3a and 3b are attached in a pivoting manner in the shown example embodiment. The positioning of the permanent magnet 6 with respect to the flange 13 is accomplished by means of a sleeve 11 in the represented case. Ball bearings 15 which serve to rotatably mount the shaft 12 of the rotor 7 are arranged in the flanges 13 and 14. Apart from the shaft 12 with its geometric axis 9, the rotor 7 comprises, as substantial components, a self-supporting hollow-cylindrical iron-free winding 8 and a collector 10 consisting of a plurality of collector segments and connected with the winding. The self-supporting hollow-cylindrical iron-free winding 8 rotates within the air gap between the surface area of the permanent magnet 6 and the inner surface of the return 16.

[0032] The hollow-cylindrical iron-free winding 8 consists of a plurality of sub-coils of the same shapes. According to the disclosure, the arrangement of the brushes and the interconnection of the sub-coils are selected in such a way that in each case, a number n≥2 of sub-coils, which are each arranged offset by 360°/n in a rotationally symmetrical manner with respect to the axis of the rotor, are supplied with the same current at the same time.

[0033] One embodiment in this respect is illustrated by the schematic representation of the coil interconnection in FIGS. 2 and 3. In the shown embodiment, the non-depicted stator has a diametrically magnetized, two-pole permanent magnet. The rotor has altogether ten sub-coils (2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2j), the collector having five collector segments (1a, 1b, 1c, 1d, 1e). The sub-coils form five pairs (2a, 20, (2c, 2h), (2e, 2j), (2g, 2b), (2i, 2d) of sub-coils each arranged in a point-symmetrical manner with respect to the rotor axis and connected in series. To this end, each sub-coil is connected to a collector segment at one end, and at the respective other end, it is connected with the diametrically opposed sub-coil. Thus, the same current each flows through diametrically opposed sub-coils due to the forced connection. It is pointed out that the picture is only of a schematical type. The sub-coils are represented by the symbol for coils. In the representation, all connections to the collector segments are to be understood as electrical connections, all line crossings, however, not as electrical connections.

[0034] Energization is effected via the two collector brushes 3a and 3b represented in FIG. 3 which are preferably designed as graphite brushes. It is particularly advantageous for the two brushes 3a and 3b to each have a width corresponding to the sum of half a collector pitch and the distance between two collector segments, wherein the two brushes 3a, 3b are arranged such that the beginning of the commutation process of the one brush occurs simultaneously with the termination of the commutation process of the respective other brush.

[0035] FIG. 4 shows an unwinding of the hollow-cylindrical iron-free winding of the embodiment of FIGS. 2 and 3 with a representation of the winding geometry and the associated interconnection of the individual sub-coils. The solid lines illustrate the connections between the collector segments (1a, 1b, 1c, 1d, le) and the sub-coils (2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2j). The broken lines illustrate the electrical connections between the sub-coils of each pair of sub-coils. The connections between the sub-coils of each pair of sub-coils can be accomplished via the coil wire itself or via the collector circuit board. For the pair of coils (2a, 2f), the current direction in the two sub-coils (2a, 2f), which are each arranged offset by 180° with respect to each other in a rotationally symmetrical manner, is illustrated by the two arrows shown in FIG. 4. In this embodiment, current consequently flows in opposite directions in the two sub-coils (2a, 2f), when viewing the respective sub-coil each in the viewing direction from the outside onto the envelope of the hollow-cylindrical iron-free winding, that means clockwise in one of the two sub-coils, and counter-clockwise in the other one of the two sub-coils.

[0036] FIG. 5 shows a circuit diagram for the rotor of an inventive four-pole DC electric motor with ten collector segments (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j) and ten sub-coils (2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2j). The sub-coils form five pairs (2a, 20, (2c, 2h), (2e, 2j), (2g, 2b), (2i, 2d) of sub-coils which are each arranged in a point-symmetrical manner with respect to the rotor axis and which are connected in series, and whose both ends are each connected with a pair of collector segments in a conductive manner. The each opposed collector segments are interconnected into five pairs (1a, 1f), (1c, 1h), (1e, 1j), (1g, 1b), (1i, 1d), so that they are on the same electrical potential by forced connection. Current flows in the same direction through the sub-coils of one pair of sub-coils in this example embodiment, in contrast to the example embodiment of FIGS. 2 to 4.

[0037] Since opposed collector segments are connected to each other, even the represented four-pole electric motor can be basically operated only with one pair of brushes. In the represented preferred design, the DC electric motor is, however, equipped with two pairs of brushes. Preferably, the same number of pairs of brushes as the number of pairs of poles should be employed in general. In the shown example embodiment, the first pair of brushes 3a, 3b is designed, analogously to the example embodiment of FIG. 3, in such a manner that the width of the brushes 3a, 3b approximately corresponds to the sum of one half collector pitch and the distance between two collector segments, wherein the two brushes 3a, 3b are arranged such that the beginning of the commutation process of the one brush 3a occurs simultaneously with the termination of the commutation process of the respective other brush 3b. The brushes 3a, 3b of the first pair of brushes consist of a material with a relatively low conductance. The second pair of brushes 3c, 3d is designed to be somewhat narrower and consists of a material having a higher conductance. Thereby, the current is reduced to a greater extent before the end of commutation, thus reducing the tendency towards sparking. Moreover, additional losses by an induced voltage already occurring during the commutation are reduced with the material which has a better conductivity. By the use of a brush with a material having a higher conductivity, losses due to the brush transition resistance are furthermore reduced.

[0038] FIG. 6 finally shows a modification of the embodiment of FIG. 4. The pairs of sub-coils are here not connected in series, but in parallel.

LIST OF REFERENCE NUMERALS

[0039] 1a to 1j collector segments [0040] 2a to 2j sub-coils [0041] 3a to 3d brushes [0042] 4 brush-commutated DC electric motor [0043] 5 stator [0044] 6 permanent magnet [0045] 7 rotor [0046] 8 hollow-cylindrical iron-free winding [0047] 9 axis [0048] 10 collector [0049] 11 sleeve [0050] 12 shaft [0051] 13 flange [0052] 14 flange (brush cover) [0053] 15 ball bearing [0054] 16 housing (magnetic return)