Brush arrangement for electric machine

Abstract

An electric machine, in particular an electric motor, wherein the electric machine has a first number (k) of commutator segments (10, 12, 14) and brushes (16, 18), wherein the commutator segments (10, 12, 14) are arranged uniformly in the circumferential direction on a circumference of a segment carrier (24), wherein the brushes (16, 18) are arranged such that, in order to reduce current ripple when using a wave winding and a number of brushes (16, 18) that is less than a pole number (2p) of the electric machine, commutation times are distributed as uniformly as possible, wherein the brushes (16, 18) comprise a first pair of brushes (16, 18), characterized in that between a first radial axis (20) of a first (16) of the brushes (16, 18) of the first pair of brushes (16, 18) and a second radial axis (22) of a second (18) of the brushes (16, 18) 18) of the first pair of brushes (16, 18) a first circumferential angle α1 exists,whose absolute value abs (α1) of a brush target spacing angle , α should = (360 ° / 2 k ) ( 2 ⋅ floor ( U2 ⋅ ( k / 2 p ) ) + 1 ) to no more than a tolerance angle α T deviates, where U2 is an odd natural number, abs () is an absolute value function, floor () is an integer rounding-down function, and α T a tolerance angle that is less than 8°.

Description

[0001] The invention relates to an electrical machine, in particular an electric motor, wherein the electrical machine has a first number of commutator segments and brushes, wherein the commutator segments are arranged uniformly distributed in the circumferential direction on a circumference of a segment carrier.

[0002] DE 695 13 655 T2 describes two windshield wiper motors, each with two speeds. One of the two motors has two poles and three brushes, with a high-speed brush offset from a common grounding brush by a circumferential angle of, for example, 120°. Here, the circumferential angle is selected depending on a desired ratio between the motor's high and low rotational speeds. The other motor has four poles and six brushes, with the high-speed brush offset from the associated grounding brush by a circumferential angle of, for example, 60°. Here, too, the circumferential angle is selected depending on the desired ratio between the motor's high and low rotational speeds.It has been observed that the operation of such conventional motors can lead to high power losses in upstream electronics, voltage fluctuations in the on-board electrical system, and electromagnetic interference (EMC) problems. This is especially true when wave winding is used and the number of brushes is fewer than the number of poles.

[0003] The generic JP S62-230340 A shows an electric motor which has an armature with armature windings, a commutator with a plurality of commutator segments, insulation material between the commutator segments and at least one pair of brushes, wherein the brushes are arranged such that the end face of the first brush is opposite an insulation material, while the end face of the second brush is in contact with a commutator segment.

[0004] JP S63-302751 A shows a flat motor having a permanent magnet field, a wave-wound flat armature, a commutator and a pair of brushes arranged at an asymmetrical position to the axis, wherein the brushes are arranged such that the center of one brush is located at the center of a commutator segment, while the center of the other brush is located at a position between -10% and +10% of the center between the commutator segments.

[0005] The invention is based on the object of reducing power losses in upstream electronics, voltage fluctuations in the vehicle electrical system, and electromagnetic interference. This object is achieved by the features of the independent claim. Advantageous embodiments of the invention are specified in the dependent claims.

[0006] The invention is based on a generic electrical machine, in particular an electric motor, in that the brushes are arranged such that, in order to reduce current ripple when using a wave winding and a number of brushes that is less than the number of poles of the electrical machine, commutation times are distributed as evenly as possible, wherein the brushes comprise a first brush pair. According to the invention, there is a first circumferential angle α1 between a first radial axis of a first of the brushes of the first brush pair and a second radial axis of a second of the brushes of the first brush pair, the absolute value of which angle abs (α1) depends on a brush target spacing angle α soll = (360° / 2k) (2 · floor (U2 · (k / 2p)) + 1) by not more than a tolerance angle α Twhere U2 is an odd natural number, abs () is an absolute value function, floor () is an integer rounding function and α T a tolerance angle which is less than 8°, in particular less than 4°, in particular less than 2°, in particular less than 1°.

[0007] In a further development of the electrical machine abs (abs (α1) - α P · U2) > α T , where α P a pole pitch angle of the electrical machine is

[0008] In a likewise preferred embodiment of the electric machine, a first absolute value of a first difference between the first circumferential angle less a first product of half a lamination pitch angle of the electric machine and a first odd natural number is smaller than a tolerance angle, wherein the first odd natural number is equal to one plus twice a third product, rounded to an integer, of a second odd natural number multiplied by a quotient of a pole pitch angle of the electric machine divided by the lamination pitch angle, wherein a second absolute value of a second difference between the first circumferential angle less a second product of the pole pitch angle of the electric machine multiplied by the second odd natural number is greater than the tolerance angle, wherein the tolerance angle is less than 8°, in particular less than 4°,in particular less than 2°, in particular less than 1°.,

[0009] A preferred embodiment provides that a half of the second odd natural number rounded up to an integer is less than or equal to a quarter of the number of poles rounded up to an integer.

[0010] In an advantageous embodiment, the first difference is positive or negative.

[0011] An equally preferred embodiment provides that twice the first quotient is not a natural number.

[0012] A preferred further development provides that the number of poles is less than 11, in particular less than 9, in particular less than 7.

[0013] Preferably, the number of commutator segments is less than 27, in particular less than 25, in particular less than 23, in particular less than 21, in particular less than 19, in particular less than 17, in particular less than 15.

[0014] The electrical machine can be designed such that the second odd natural number is less than 10, in particular less than 8, in particular less than 6, in particular less than 4, in particular less than 2.

[0015] A further embodiment provides that the first odd natural number is equal to five and the second odd natural number is equal to one, in particular wherein the first product is equal to 64.3° or equal to 34.6°.

[0016] Furthermore, an electrical machine is preferred in which a rotor and / or a stator of the electrical machine has a wave winding, in particular a single-start wave winding.

[0017] The electric machine can be a servo motor or a wiper motor

[0018] The invention will now be explained with reference to the accompanying figures using particularly preferred embodiments.

[0019] They show: Fig. 1a to 1c show a schematic diagram of a brush arrangement according to a first embodiment of the invention; Fig. 2a to 2c show a schematic diagram of a brush arrangement according to a second embodiment of the invention; Fig. 3 a schematic diagram of an undesired unevenly distributed current waveform as a function of a rotor position and a desired evenly distributed current waveform as a function of the rotor position; and Fig. 4a to 4c are schematic diagrams of three possible arrangements of angular tolerance ranges of a brush arrangement according to the invention in relation to a conventional brush arrangement.

[0020] When using a wave winding, a number of brushes smaller than the pole number 2p can be selected without additional measures, which only slightly changes the characteristic curve of the electrical machine. Fig. In the brush arrangement shown in Figure 1a for a crossed single-start wave winding of a 6-pole motor with 14 commutator segments 10, 12, 14 and two brushes 16, 18, a first circumferential angle α1 between a first radial axis 20 of the first brush 16 and a second radial axis 22 of the second brush 18 is approximately 64.3°. The second brush 18 is positioned symmetrically to two commutator segments 10, 12 (see Fig. 1c), when the rotor 24 has a rotor position 26 (see Fig. 3) in which the first brush 16 is positioned centrally on a third commutator bar 14 (see Fig. 1b). In the following, the term "bar" is used instead of "commutator bar." It is often advisable to arrange two brushes 16, 18 at the smallest possible angle α1 to each other to save space.

[0021] In the Fig. In the brush arrangement shown in Figure 2 for a crossed single-start wave winding of a 10-pole motor with 26 commutator segments 10, 12, 14 and two brushes 16, 18, a first circumferential angle α1 between a first radial axis 20 of the first brush 16 and a second radial axis 22 of the second brush 18 is approximately 34.6°. The second brush 18 is positioned symmetrically to two commutator segments 10, 12 (see Fig. 4c), when the rotor 24 has a rotor position 26 (see Fig. 3) in which the first brush 16 is positioned centrally on a third commutator bar 14 (see Fig. 4b).

[0022] Table 1 provides an overview of the characteristics of the Fig. 1 and Fig. 2, wherein the column “No” is the serial number of the embodiment, the column “k” is the number of commutator segments k, the column “2p” is the number of poles 2p, the column “U2” is the second odd natural number U2, the column “α K / 2“ half the α K / 2 slat pitch angle α K , the column “Q1” the first quotient Q1, the column “U1” the first odd natural number U1 and the column “α soll “ the brush target distance angle α soll contains. Table 1 No k 2p U2 α K / 2 = 360° / 2k Q1 = k / 2p U1 α soll = U1 * α K / 2 1 14 6 1 12,86° 2,33 5 64,3° 2 26 10 1 6.92° 2,60 5 34,6°

[0023] The brush spacing angle α soll for further embodiments, ie for other triples of number of lamellas k, number of poles 2p and second odd natural number U2 can be determined as follows: α soll = U1 * α K / 2 with U1 := 2 [U2 * Q1] + 1 = 1 + 2 * P3 with P3 := [U2 * Q1], where the square bracket represents the Gaussian bracket function (ie, rounding or integer function). Half α K / 2 slat pitch angle α K is equal to the full angle 360° divided by twice 2k the number of lamellas k. The quotient Q1 is equal to a pole pitch angle α P= 360° / 2p of the electrical machine divided by the lamination angle α K = 360° / k and is also equal to the number of lamellae k divided by the number of poles 2p. The first odd natural number U1 is equal to one plus twice 2[P3] of a third product P3, rounded to an integer [P3], of the odd natural number U2 multiplied by the quotient Q1.

[0024] The following explains why the electrical machine according to the invention reduces power losses in upstream electronics, voltage fluctuations in the vehicle electrical system and electromagnetic interference. Fig. 3 shows a current waveform 36 across the rotor position 26, as can be measured on the supply lines of a conventional electrical machine. The current waveform 36 is periodic, but has amplitudes 38, 40 of varying magnitudes. The amplitudes 38, 40 and, in particular, their fluctuations 41 are a measure of current ripple. The higher the current ripple, the higher the power losses in upstream electronics, voltage fluctuations in the vehicle electrical system, and electromagnetic interference. The high current ripple of the conventional electrical machine can be caused by an uneven distribution 50 of the commutation positions 42 or times 42. In contrast, the current waveform 44 of an electrical machine according to the invention does not have such strong fluctuations 41 in the amplitude 46. This means that the current ripple is significantly lower than in the conventional electrical machine.The technical reason for this is the more uniform distribution 52 of the brushes 16, 18, 28, 30 with respect to the lamination pitch of the commutator. Thus, according to the invention, the current ripple is reduced by distributing the commutation positions 48 or times 48 evenly (or at least more evenly) than in conventional electrical machines. The brushes 16, 18 of a brush pair 16, 18 are optimally arranged with respect to current ripple when the two brushes 16, 18 alternately commutate with time symmetrical relationship to one another. This condition is met when the two brushes 16, 18 are arranged geometrically symmetrically with respect to the lamination arrangement. This is the case when an adjacent pair 10, 12 of two lamellae 10, 12 is arranged centrally under the radial axis 22 of the second brush 18, when a third lamella 14 is arranged centrally under the radial axis 20 of the first brush 16.The brush arrangement according to the invention is based on the approach of a desired brush spacing angle α. soll an odd natural number U1 of half α K / 2 slat pitch angles α K This means that the brush spacing angle α soll equal to one current reversal step plus or minus half an α K / 2 slat pitch angle α K .

[0025] There are conventional brush assemblies that, for other reasons, exactly or approximately meet this dimensioning rule. Such conventional brush assemblies are excluded from the subject matter of the brush assembly according to the invention, whereby the claimed brush assemblies are new compared to such conventional brush assemblies. Table 2 contains an overview of features of two conventional embodiments that correspond to the first and second embodiments according to the invention, wherein the column "No" represents the serial number of the embodiment, the column "2p" the number of poles 2p, the column "α P “ the pole pitch angle α P , the column “U2” the second odd natural number U2 and the column “α konv “ a conventional brush pitch angle α konv contains. Table 2 No 2p α P = 360° / 2p U2 α konv = U2 * α P 1 6 60° 1 60° 2 10 36° 1 36°

[0026] The conventional brush pitch angle α konvfor further corresponding embodiments, ie for other 2-tuples of pole number 2p and second odd natural number U2 can be calculated as follows: α konv = U2 * α P . The conventional brush pitch angle α konv is therefore equal to a second product of the pole pitch angle α P of the electrical machine multiplied by the second odd natural number U2. The conventional brush arrangement is based on the idea of ​​assigning an integer number of pole pitches α to a current reversal step. P to assign.

[0027] Fig. 4a shows a first angular tolerance range 54 for a brush arrangement according to the invention, which does not overlap with a second angular tolerance range 56 of a corresponding conventional brush arrangement. In this case, all brush arrangements α 11 , α 12 , α 13within the first angular tolerance range 54 a new brush arrangement α 11 , α 12 , α 13 represents. Fig. Figure 4b shows a second angle tolerance range 56 for a conventional brush arrangement, which overlaps part of the first angle tolerance range 54, but not the brush target pitch angle α soll In this case, only those brush arrangements α 11 , α 12 a new brush arrangement α 11 , α 12 which lie both within the first angular tolerance range 54 and outside the second angular tolerance range 56. Fig. 4c shows a second angle tolerance range 56 for a conventional brush arrangement, which overlaps part of the first angle tolerance range 54 and even the brush target distance angle α soll . In this case too, only those brush arrangements α 11 a new brush arrangement α 11which are both within the first angle tolerance range 54 and outside the second angle tolerance range 56. In the brush arrangement according to the invention, a first absolute value B1 of a first difference D1 from the first circumferential angle α1 less the brush target distance angle α soll smaller than a tolerance angle α T . At the same time, a second absolute value B2 of a second difference D2 from the first circumferential angle α1 minus a second product α konv from the pole pitch angle α P of the electrical machine multiplied by the second odd natural number U2 is greater than the tolerance angle α T . The tolerance angle α T may be less than 8°, in particular less than 4°, in particular less than 2°, in particular less than 1°.

[0028] Using the above dimensioning rules, the person skilled in the art can, for example with the aid of a spreadsheet program, calculate a table which, for a large number of tuples from a given tolerance angle α T , number of lamellas k, number of poles 2p, second odd natural number U2 and pole pitch angle α P In order to avoid including a comprehensive tabular overview for economic reasons, the following is noted: In particular, in the case of a so-called "accidental anticipation," all angular tolerance ranges calculable using the above dimensioning rules should not only be considered disclosed in their entirety, but each of the angular tolerance ranges calculable in this way should also be considered disclosed (at least implicitly) in isolation.

[0029] The load on the electric machine can be mechanical, while the drive is electric (motor operation). Alternatively or additionally, the electric machine can be mechanically driven, while the load on the electric machine is electric (generator operation).

Claims

[1] Electrical machine, in particular an electric motor, wherein the electrical machine has a first number (k) of commutator segments (10, 12, 14) and brushes (16, 18), wherein the commutator segments (10, 12, 14) are arranged uniformly distributed in the circumferential direction on a circumference of a segment carrier (24), wherein the brushes (16, 18) are arranged such that, in order to reduce a current ripple when using a wave winding and a number of brushes (16, 18) which is smaller than a number of poles (2p) of the electrical machine, commutation times are distributed as evenly as possible, wherein the brushes (16, 18) comprise a first pair of brushes (16, 18), characterized bythat between a first radial axis (20) of a first (16) of the brushes (16, 18) of the first brush pair (16, 18) and a second radial axis (22) of a second (18) of the brushes (16, 18) of the first brush pair (16, 18) there is a first circumferential angle α1, the absolute value of which abs (α1) deviates from a brush target distance angle αset=(360° / 2k)(2⋅floor(U2⋅(k / 2p))+1) by no more than a tolerance angle α T where U2 is an odd natural number, abs () is an absolute value function, floor () is an integer rounding function and α T a tolerance angle that is less than 8°. [2] Electrical machine according to claim 1, characterized by , that abs (abs(α1)−αP⋅U2)>αT is, where α P is a pole pitch angle of the electrical machine. [3] Electrical machine according to one of claims 1 to 2, in particular an electric motor, wherein the electrical machine has a first number (k) of commutator segments (10, 12, 14) and a pair of brushes (16, 18), wherein the commutator segments (10, 12, 14) are arranged in a circumferential direction uniformly distributed on a circumference of a segment carrier (24), wherein a first radial axis (20) of a first (16) of the brushes (16, 18) and a second radial axis (22) of a second (18) of the brushes (16, 18) enclose a first circumferential angle (α1) between them, characterized by that a first absolute value (B1) of a first difference (D1) from the first circumferential angle (α1) less a first product (α soll ) of half (α K / 2) Slat pitch angle (α K ) of the electrical machine with a first odd natural number (U1) is smaller than a tolerance angle (α T), where the first odd natural number (U1) is equal to one plus twice (2[P3]) a third product (P3), rounded to an integer ([P3]), of a second odd natural number (U2) multiplied by a quotient (Q1) of a pole pitch angle (α P ) of the electrical machine divided by the lamination angle (α K ), wherein a second absolute value (B2) of a second difference (D2) from the first circumferential angle (α1) less a second product (α konv ) from the pole pitch angle (α P ) of the electrical machine multiplied by the second odd natural number (U2) is greater than the tolerance angle (α T ), where the tolerance angle (α T ) is less than 8°. [4] Electrical machine according to one of claims 1 to 3, characterized bythat a half (U2 / 2) of the second odd natural number (U2) rounded up to an integer ([(U2 / 2)+ (1 / 2)]) is less than or equal to a quarter (p / 2) of the number of poles (2p) rounded up to an integer ([(p / 2) + (1 / 2)]). [5] Electrical machine according to claim 3 or 4, characterized by that the first difference (D1) is positive or negative. [6] Electrical machine according to one of claims 3 to 5, characterized by that twice (2Q1) the first quotient (Q1) is not a natural number. [7] Electrical machine according to one of claims 1 to 6, characterized by that the number of poles (2p) is less than 11. [8] Electrical machine according to one of claims 1 to 7, characterized by that the number of commutator segments (k) is less than 27. [9] Electrical machine according to one of claims 1 to 8, characterized by that the second odd natural number (U2) is less than 10. [10] Electrical machine according to one of claims 3 to 9, characterized by that the first odd natural number (U1) is equal to five and the second odd natural number (U2) is equal to one. [11] Electrical machine according to one of claims 1 to 10, characterized by that a rotor (24) and / or a stator of the electrical machine has a wave winding. [12] Electrical machine according to one of claims 1 to 11, characterized by that the electric machine is a servo motor or a wiper motor.

Images