Brushed Commutated DC Motor with Improved Oscillation Performance

Abstract

The present invention relates to a brushed commutated DC motor having a stator and a rotor, the stator comprising a permanent magnet having p pole pairs, and the rotor being rotatable relative to the stator and having a hollow cylindrical ironless winding having a geometric axis and Q sub-coils, and a collector having K collector segments, wherein the sub-coils are distributed on the outer periphery of the rotor, and wherein the brushed commutated DC motor further has at least one pair of brushes in contact with the collector and energizes the sub-coils through these brushes. According to the invention, the arrangement of the brushes and the interconnection of the sub-coils are selected in such a way that in each case, n≥2 sub-coils are simultaneously supplied with the same current, and each sub-coil is arranged offset by 360° / n in a rotationally symmetric manner with respect to the axis of the rotor.

Description

[0001] The present invention relates to a brushed commutation DC motor according to the preamble of independent claim 1.

[0002] A general brushed commutation DC motor has a stator and a rotor. The stator includes a permanent magnet having p pole pairs, and the rotor can rotate relative to the stator. The rotor has a hollow cylindrical ironless winding having a geometric axis and Q sub-coils, and a collector having K collector segments. The sub-coils are distributed on the outer periphery of the rotor, and the brushed commutation DC motor also has at least one pair of brushes in contact with the collector, and the sub-coils are energized through these brushes.

[0003] The stator of such a brushed commutation motor can have a cylindrical permanent magnet disposed inside the hollow cylindrical ironless winding. Outside, there is usually a magnetic return sleeve, which also serves as the motor housing. Due to the ironless winding, this motor has no cogging torque, so smooth operation can be achieved even at low speeds. This involves little vibration and noise. Due to the lack of iron in the rotor, there is no iron loss, and an external magnetization is continuously generated. This results in high efficiency. Moreover, even at high currents, the torque generated is still proportional to the motor current. The low inertia of the rotor mass, which results in high dynamics and short start-up times, is also advantageous.

[0004] Although brushed commutation DC motors are widely used and generally have good operating performance, in practice, it has been shown that oscillations occasionally occur in the collector region, so that the current is modulated, thus leading to an increase in the oscillations caused by this feedback. Because in a brushed commutation DC motor, during commutation, the current in the sub-coil is initially blocked by short-circuiting it via the brush, and then reset with the opposite sign. Especially in the case of a two-pole motor with sub-coils having chords or chamfers, a radial resultant force or a torque acting transversely to the axis of rotation is involved. Both of these effects can cause the rotor to deflect radially near the collector.

[0005] A brushed commutation DC motor according to the preamble of independent claim 1 is known, for example, from EP3171498 B1. This document deals with the attempt to counteract the above effects by arranging the coil plane of the sub-coil to rotate around the axis of the rotor at a correction angle between 45° and 135° relative to the collector plane of the associated collector segment. However, it has been found that oscillations and the resulting current modulation cannot be completely prevented in this way.

[0006] Therefore, the object of the present invention is to provide a general brushed commutation DC motor in which the problems shown are avoided as completely as possible.

[0007] This object is achieved by the features of independent claim 1. Thus, in a brushed commutated DC motor according to the preamble of independent claim 1, if the arrangement of the brushes and the interconnection of the sub-coils are selected in such a way that in each case n≥2 sub-coils are always supplied with the same current, where each sub-coil is arranged with a rotational symmetry with respect to the axis of the rotor and is offset by 360° / n, a solution to the problem according to the invention is given. This is to be understood as meaning that each of the n≥2 sub-coils is arranged with a rotationally symmetric offset, and each sub-coil is mapped onto itself by a rotation of 360° / n about the axis of the rotor. Of course, here only the exact mapping of the sub-coil onto itself is given, provided that the sub-coil has a uniform shape according to the preferred embodiment described below. "The same current" means the amount of electric current. Thus, the sub-coils through which "the same current" flows can be connected in series or in parallel.

[0008] In an advantageous embodiment, the sub-coil has a uniform shape at least in one projection on the surface of the hollow cylindrical ironless winding.

[0009] In order to prevent oscillations as completely as possible, it is advantageous for the shapes of the individual coils to be exactly the same. The uniform design of the sub-coils is completely variable. Suitable shapes are known, for example, from EP1780871A1, DE1801263A1, and DE1188709B. The current can flow in the same direction through n coils, which are arranged with rotational symmetry with respect to each other and are supplied with the same current simultaneously. However, embodiments are also possible in which the current can flow in opposite directions through n coils, which are arranged with rotational symmetry with respect to each other and are supplied with the same current simultaneously. As the brushes, graphite brushes are preferably used. The hollow cylindrical ironless winding is preferably self-supporting, and the sub-coils are preferably not wound around an iron core or the like.

[0010] Further preferred embodiments of the invention are the subject matter of the dependent claims.

[0011] In order to supply the same current to n sub-coils, according to an embodiment of the invention, each of the n sub-coils is arranged with rotational symmetry with respect to each other and is always energized simultaneously, and the sub-coils can be connected in series. The connection of the series-connected sub-coils can be accomplished by the coil wires themselves or by a current collector. In the latter case, the connection of the series-connected sub-coils is preferably achieved through the current collector circuit board of the current collector.

[0012] If magnetic fluxes of the same amplitude and phase always symmetrically flow through the sub-coils, the start and end of the n sub-coils are at the same electric potential, and the supply of the same current can also be achieved. According to an alternative embodiment of the present invention, the n sub-coils can be connected in parallel, and each sub-coil is arranged in a rotationally symmetric manner relative to each other and is always energized simultaneously.

[0013] The present invention is particularly applicable to a brushed commutated DC motor having a single pole pair. According to an embodiment of the present invention, the number of pole pairs p is thus 1, where the collector has an odd number K≥3 of collector segments, where the number Q of sub-coils is 2·K, and where the number n of each sub-coil arranged in a rotationally symmetric manner relative to each other and always energized simultaneously is 2. The two coils energized simultaneously are radially opposite and are preferably connected in series. According to a particularly preferred and easily implementable embodiment of the present invention, in this case, each sub-coil is connected to one collector segment at one end and is connected to the radially opposite sub-coil at the corresponding other end.

[0014] The present invention is also applicable to a brushed commutated DC motor having more than one pair of pole pairs. According to an embodiment of the present invention, the number of pole pairs p is thus greater than 1, where the collector has a number K = k·p of collector segments, where k is an odd number ≥3, where the number Q of sub-coils is q·p, where the number q either corresponds to the number k or corresponds to twice the number k, and where the number n of each sub-coil arranged in a rotationally symmetric manner relative to each other and each energized simultaneously corresponds to the number p if q = k, or corresponds to twice p if q = 2·k, where each of the p collector segments is conductively connected to each other on the rotor side, and each of the collector segments is also arranged to be offset by 360° / p in a rotationally symmetric manner relative to the axis of the rotor.

[0015] According to another particularly preferred embodiment of the present invention, each of the two brushes in the pair of brushes has a width corresponding to the sum of half of the collector pitch and the distance between two collector segments, and the two brushes are arranged such that the start of the commutation process of one brush in the pair coincides with the termination of the commutation process of the corresponding other brush in the pair. Thus, the above-mentioned negative effects are further reduced. The width of the brush refers to the width exactly at the outer circumference of the collector (i.e., at the contact surface between the brush and the collector). Therefore, the actual width corresponds to the chord generated by half of the pitch and the distance.

[0016] In a brushed-commutated DC motor having more than one unipolar pair, according to another particularly preferred embodiment of the invention, the pair of brushes can also be a first pair of brushes, wherein the brushed-commutated DC motor further comprises at least another pair of brushes also in contact with the collector, wherein each of the two brushes of the other pair of brushes has a width smaller than the brush width of the first pair of brushes. Here, it is particularly advantageous that the brushes of at least one additional pair of brushes are made of a material having a higher electrical conductivity than the material of the brushes constituting the first pair of brushes.

[0017] Thus, the current is reduced to a greater extent before the commutation ends, thereby reducing the tendency to generate sparks. In addition, using a material with better electrical conductivity can reduce the additional losses caused by the induced voltage that has already appeared during commutation. By using brushes made of a material with a higher electrical conductivity, the losses caused by the brush transition resistance are further reduced.

[0018] According to another particularly preferred embodiment of the invention, all sub-coils have the same shape. Thereby, the negative effects described at the beginning can be most effectively avoided.

[0019] As described above, the present invention is particularly applicable to a brushed-commutated DC motor whose rotor has sub-coils, and these sub-coils are designed in a chordal and / or chamfered manner with respect to the axis of the rotor.

[0020] The embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

[0021] In the drawings:

[0022] Figure 1 A schematic exploded view of a brushed-commutated DC motor is shown,

[0023] Figure 2 A schematic diagram showing the interconnection of sub-coils of a two-pole brushed-commutated DC motor according to a first embodiment of the present invention is shown,

[0024] Figure 3 Shows Figure 2 The representation of and additional brushes shown,

[0025] Figure 4 Shows Figure 2 And 3 The development of a hollow cylindrical ironless winding of an embodiment of, having a representation of the winding geometry and the relevant interconnection of individual sub-coils,

[0026] Figure 5 A schematic diagram showing the interconnection of sub-coils of a four-pole brushed-commutated DC motor according to a second embodiment of the present invention is shown, and

[0027] Figure 6Shows a schematic diagram of the interconnection of sub-coils of a four-pole brushed commutated DC motor according to a third embodiment of the present invention.

[0028] In the following figures, the same parts are denoted by the same reference numerals. If the figures contain reference numerals that are not discussed in more detail in the relevant description of the figures, reference is made to the description before or after the figures.

[0029] First, regarding Figure 1 , the general structure of the brushed commutated DC motor 4 is shown. The main components of the DC motor 4 with a non-ferrous winding are a stator 5 and a rotor 7 rotatably mounted relative to the stator. The stator 5 includes a permanent magnet 6 as a main component, which can be of a hollow cylindrical design, a flange 13 for positioning the permanent magnet 6, a magnetic circuit 16 made of iron and serving as a housing, and a further flange 14, which in the exemplary embodiment shown serves as a brush or housing cover and to which two collector brushes 3a and 3b are pivotally attached. In the case shown, the positioning of the permanent magnet 6 relative to the flange 13 is achieved by means of a sleeve 11. Ball bearings 15 for the rod 12 for rotatably mounting the rotor 7 are arranged in the flanges 13 and 14. In addition to the rod 12 having its geometric axis 9, the rotor 7 includes a self-supporting hollow cylindrical non-ferrous winding 8 as a main component and a collector 10 consisting of a plurality of collector segments and connected to the winding. The self-supporting hollow cylindrical non-ferrous winding 8 rotates in the air gap between the surface area of the permanent magnet 6 and the inner surface of the circuit 16.

[0030] The hollow cylindrical non-ferrous winding 8 consists of a plurality of sub-coils of the same shape. According to the present invention, the arrangement of the brushes and the interconnection of the sub-coils are selected in such a way that in each case, n≥2 sub-coils are supplied with the same current at the same time, where each sub-coil is arranged with a rotation symmetry relative to the axis of the rotor and is offset by 360° / n.

[0031] An embodiment in this regard is through Figure 2 and 3is illustrated by a schematic representation of the coil interconnections. In the illustrated embodiment, the stator, which is not depicted, has a radially magnetized two-pole permanent magnet. The rotor has a total of ten sub-coils (2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2j), and the current collector has five current collector segments (1a, 1b, 1c, 1d, 1e). The sub-coils form five pairs (2a,2f), (2c,2h), (2e,2j), (2g,2b), (2i,2d), and each pair of sub-coils is arranged in a point-symmetric manner with respect to the axis of the rotor and connected in series. For this purpose, each sub-coil is connected to a current collector segment at one end, and at the corresponding other end, it is connected to the radially opposite sub-coil. Thus, due to the forced connection, the same current flows through the radially opposite sub-coils respectively. It should be noted that this figure is only a schematic type of figure. The sub-coils are represented by coil symbols. In this illustration, all connections to the current collector segments should be understood as electrical connections. However, all line crossings are not understood as electrical connections.

[0032] Power-on is achieved by Figure 3 the two current collector brushes 3a and 3b shown, which are preferably designed as graphite brushes. Particularly advantageously, each of the two brushes 3a and 3b has a width corresponding to the sum of half of the current collector spacing and the distance between two current collector segments, and the two brushes 3a, 3b are arranged such that the start of the commutation process of one brush occurs simultaneously with the termination of the commutation process of the corresponding other brush.

[0033] Figure 4 is shown Figure 2 and 3 the unfolding of a hollow cylindrical ironless winding of the embodiment of, which has a representation of the winding geometry and the relevant interconnections of the individual sub-coils. The solid lines represent the connections between the current collector segments (1a, 1b, 1c, 1d, 1e) and the sub-coils (2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2j). The dashed lines represent the electrical connections between the sub-coils of each pair of sub-coils. The connection between the sub-coils of each pair of sub-coils can be achieved by the coil wire itself or through the current collector circuit board. For the pair of coils (2a, 2f), the current directions in the two sub-coils (2a, 2f) are shown by two arrows in Figure 4 and the two sub-coils are arranged such that they are offset from each other by 180° in a rotationally symmetric manner. In this embodiment, when observing the individual sub-coils in the viewing direction from the outside to the surface of the hollow cylindrical ironless winding, the current thus flows in opposite directions in the two sub-coils (2a, 2f), which means clockwise in one of the two sub-coils and counterclockwise in the other of the two sub-coils.

[0034] Figure 5Shows the circuit diagram of the rotor of a creative four - pole DC motor having 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 of sub - coils (2a, 2f), (2c, 2h), (2e, 2j), (2g, 2b), (2i, 2d), each pair of sub - coils being arranged symmetrically with respect to the rotor axis in a point - symmetric manner and connected in series, and their ends being conductively connected to a pair of collector segments respectively. Each pair of opposite collector segments is interconnected into five pairs (1a, 1f), (1c, 1h), (1e, 1j), (1g, 1b), (1i, 1d), so that they are at the same electric potential through forced connection. Compared with Figures 2 to 4 the example embodiment of, in which example embodiment, current flows through the sub - coils of a pair of sub - coils in the same direction.

[0035] Since the opposite collector segments are connected to each other, even the shown four - pole motor can be operated basically with only one pair of brushes. However, in the shown preferred design, the DC motor is equipped with two pairs of brushes. Preferably, the same number of brush pairs as the number of pole pairs should generally be used. In the shown example embodiment, the first pair of brushes 3a, 3b is designed in such a way as to be similar to Figure 3 the example embodiment of: such that the widths of the brushes 3a, 3b roughly correspond to the sum of half of the collector spacing and the distance between two collector segments, where the two brushes 3a, 3b are arranged such that the start of the commutation process of one brush 3a coincides with the termination of the commutation process of the corresponding other brush 3b. The brushes 3a, 3b of the first pair of brushes are made of a material with relatively low electrical conductivity. The second pair of brushes 3c, 3d is designed to be slightly narrower and is composed of a material with higher electrical conductivity. Thus, the current is reduced to a greater extent before the end of commutation, thereby reducing the tendency to generate sparks. In addition, using a material with better conductivity can reduce the additional losses caused by the induced voltage that has appeared during commutation. By using brushes made of a material with higher conductivity, the losses due to the brush transition resistance are further reduced.

[0036] Figure 6 Finally, there is shown Figure 4 a modification of the embodiment of. Here, the pairs of sub - coils are not connected in series but in parallel.

[0037] List of reference numerals

[0038] 1a to 1j Collector segments

[0039] 2a to 2j Sub - coils

[0040] 3a to 3d Brushes

[0041] 4 Brushed Commutated DC Motor

[0042] 5 Stator

[0043] 6 Permanent Magnet

[0044] 7 Rotor

[0045] 8 Hollow Cylindrical Ironless Winding

[0046] 9 Shaft

[0047] 10 Current Collector

[0048] 11 Sleeve

[0049] 12 Rod

[0050] 13 Flange

[0051] 14 Flange (Brush Cover)

[0052] 15 Ball Bearing

[0053] 16 Housing (Magnetic Circuit)

Claims

1. A brushed commutated DC motor (4) having a stator (5) and a rotor (7), said stator (5) including permanent magnets (6) having a number p of pole pairs, and said rotor (7) being rotatable relative to said stator (5), said rotor (7) having a hollow cylindrical ironless winding (8) having a geometric axis (9) and Q sub-coils (2a - 2j), and a collector (10) having K collector segments (1a - 1j), wherein the sub-coils (2a - 2j) are distributed on the outer circumference of the rotor (7), and wherein the brushed commutated DC motor (4) further has at least one pair of brushes (3a - 3d) which contact the collector (10) and energize the sub-coils (2a - 2j) through it, characterized in that, The arrangement of the brushes (3a - 3d) and the interconnection of the sub - coils (2a - 2j) are selected in such a way that in each case, for n≥2 sub - coils (2a - 2j), the same current is always supplied simultaneously, and each sub - coil is arranged with an offset of 360° / n in a rotationally symmetric manner with respect to the geometric axis (9) of the rotor (7). Wherein the number of pole pairs p is greater than 1, wherein the collector (10) has a number K = k·p of collector segments (1a - 1j), where k is an odd number ≥3, wherein the number Q of sub - coils (2a - 2j) is q·p, where the number q either corresponds to the number k or twice the number k, and wherein if q = k, the number n of each sub - coil (2a - 2j) arranged in a rotationally symmetric manner with respect to each other and simultaneously energized corresponds to the number p, or if q = 2·k, the number n corresponds to twice p, and wherein the p collector segments (1a - 1j) are conductively connected to each other on the rotor side, and each of the collector segments is also arranged with an offset of 360° / p in a rotationally symmetric manner with respect to the geometric axis (9) of the rotor (7).

2. The brushed commutated DC motor (4) according to claim 1, characterized in that, The sub - coils (2a - 2j) have a uniform shape at least in one projection on the surface of the hollow cylindrical ironless winding (8).

3. The brushed commutated DC motor (4) according to claim 1 or 2, characterized in that, Each of the n sub - coils (2a - 2j) arranged in a rotationally symmetric manner with respect to each other and always simultaneously energized is connected in series.

4. The brushed commutation DC motor (4) according to claim 1 or 2, characterized in that, Each of the n sub - coils (2a - 2j) arranged in a rotationally symmetric manner with respect to each other and always simultaneously energized is connected in parallel.

5. The brushed commutated DC motor (4) according to claim 1, characterized in that, The number of pole pairs p is 1, wherein the collector (10) has an odd number K≥3 of collector segments (1a - 1j), wherein the number Q of sub - coils is 2·K, and wherein the number n of each sub - coil (2a - 2j) arranged in a rotationally symmetric manner with respect to each other and always simultaneously energized is 2.

6. The brushed commutated DC motor (4) according to claim 5, characterized in that, One end of each sub - coil (2a - 2j) is connected to a collector segment (1a - 1j), and at the corresponding other end is connected to a radially opposite sub - coil (2a - 2j).

7. The brushed commutation DC motor (4) according to claim 1, characterized in that, The width of two brushes (3a, 3b) of the pair of brushes corresponds to the sum of half of the collector pitch and the distance between two collector segments (1a - 1j), and the two brushes (3a, 3b) are arranged such that the start of the commutation process of one brush (3a, 3b) of the pair coincides with the termination of the commutation process of the corresponding other brush (3a, 3b) of the pair.

8. The brushed commutated DC motor (4) according to claim 7, characterized in that, The pair of brushes (3a, 3b) is the first pair of brushes (3a, 3b), wherein the brushed commutation DC motor (4) further includes at least another pair of brushes (3c, 3d) that also contact the collector (10), and the width of each of the two brushes (3c, 3d) of the other pair of brushes (3c, 3d) is less than the width of the brushes (3a, 3b) of the first pair of brushes (3a, 3b).

9. The brushed commutation DC motor (4) according to claim 8, characterized in that, The brushes (3c, 3d) of the at least another pair of brushes (3c, 3d) are made of a material having a higher electrical conductivity than the material of the brushes (3a, 3b) constituting the first pair of brushes (3a, 3b).

10. The brushed commutated DC motor (4) according to claim 1, characterized in that, All of the sub-coils (2a - 2j) have the same shape.

11. The brushed commutation DC motor (4) according to claim 1, characterized in that, The sub-coils (2a - 2j) are designed to be chorded and / or chamfered with respect to the geometric axis (9) of the rotor (7).

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