Patent Application
20120133240
The invention relates to an electrical machine, in particular an electric motor wherein the electrical machine has a first number of commutator laminates and brushes, wherein the commutator laminates are arranged distributed uniformly in the circumferential direction on a circumference of a laminate support.
DE 695 13 655 T2 describes two windshield wiper motors for two speeds in each case. One of the two motors has two poles and three brushes, with a high-speed brush being arranged offset through a circumferential angle of, for example 120° with respect to a common grounding brush. Here, the circumferential angle is chosen as a function of a desired ratio between a high speed and a low speed of the motor. The other motor has four poles and six brushes, with the high-speed brush being arranged offset through a circumferential angle of, for example, 60° with respect to the associated grounding brush, and with the circumferential angle also being chosen here as a function of the desired ratio between a high speed and a low speed of the motor. It has been found that the operation of such conventional motors can lead to high power losses in upstream electronics, to voltage fluctuations in a vehicle power supply system, and to electromagnetic interference (EMC problems). This is particularly the case when a wave winding is used, and the number of brushes is less than the number of poles.
The invention is based on the object of reducing power losses in upstream electronics, voltage fluctuations in the vehicle power supply system and electromagnetic interference.
The invention builds on an electrical machine of this generic type, in particular an electric motor, in that the brushes are arranged such that commutation times are distributed as uniformly as possible in order to reduce the current ripple when using a wave winding and a number of brushes which is less than the number of poles in the electrical machine.
One embodiment of the electrical machine provides that the brushes comprise a first brush pair, wherein a first circumferential angle α1 exists between a first radial axis of a first of the brushes in the first brush pair and a second radial axis of a second of the brushes in the first brush pair, the absolute magnitude abs (α1) of which first circumferential angle α1 differs from a brush nominal separation angle αnom =(360°/2k) (2·floor(U2·(k/2p))+1) by no more than a tolerance angle αT, where U2 is an odd natural number, abs ( ) is an absolute magnitude function, floor ( ) is an integer rounding function and αT is a tolerance angle, which is less than 8°, in particular less than 4°, in particular less than 2°, in particular less than 1°.
In one development of the electrical machine, abs(abs(α1)−αP·U2)>αT where αP is a pole pitch angle of the electrical machine.
In a likewise preferred embodiment of the electrical machine, a first absolute magnitude of a first difference from the first circumferential angle minus a first product of half of the laminate pitch angle of the electrical machine with a first odd natural number is less 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 electrical machine divided by the laminate pitch angle, wherein a second absolute magnitude of a second difference from the first circumferential angle minus a second product from the pole pitch angle of the electrical 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°.
One preferred embodiment provides that a half of the second odd natural number rounded to an integer is less than or equal to a quarter of the number of poles rounded to an integer.
In one advantageous embodiment, the first difference is positive or negative.
A likewise preferred embodiment provides that twice the first quotient is not a natural number.
One preferred development provides that the number of poles is less than 11, in particular less than 9, in particular less than 7.
Preferably, the number of commutator laminates 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.
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.
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 with the first product being equal to 64.3° or equal to 34.6°.
In addition, an electrical machine is preferred in which a rotor and/or a stator of the electrical machine has a wave winding, in particular a simplex wave winding.
The electrical machine may be a servomotor or a wiper motor.
The invention will now be explained using particularly preferred embodiments and with reference to the accompanying figures, in which:
a to 1c show a schematic illustration of a brush arrangement according to a first exemplary embodiment of the invention;
a to 2c show a schematic illustration of a brush arrangement according to a second exemplary embodiment of the invention;
a to 4c show schematic illustrations of three possible arrangements of angle tolerance ranges of a brush arrangement according to the invention, related to a conventional brush arrangement.
When using a wave winding, it is possible to choose a number of brushes less than the number of poles 2p without additional measures, with the characteristic of the electrical machine being changed only slightly. In the brush arrangement shown in
In the brush arrangement shown in
Table 1 contains an overview of features of the embodiments illustrated in
For further embodiments, that is to say for other triple sets of the number of laminates k, the number of poles 2p and the second odd natural number U2, the brush nominal separation angle αnom can be determined as follows: αnom=U1*αK/2 where U1:=2[U2*Q1]+1=1+2*P3 where P3:=[U2*Q1], with the square parentheses representing the rounding function (that is to say the rounding or integer function). Half αK/2 the laminate pitch angle αK is equal to the complete angle 360° divided by twice 2k the number of laminates k. The quotient Q1 is equal to a pole pitch angle αP=360°/2p of the electrical machine divided by the laminate pitch angle αK=360°/k, and is also equal to the number of laminates k divided by the number of poles 2p. The first odd natural number U1 is equal to one plus twice 2[P3] a third product P3 rounded to an integer [P3], from the odd natural number U2 multiplied by the quotient Q1.
The following text explains why the electrical machine according to the invention reduces power losses in upstream electronics, voltage fluctuations in the vehicle power supply system, and electromagnetic interference.
Table 2 contains an overview of features of two conventional embodiments which correspond to the first and second embodiments according to the invention, with the column “No” containing the order number of the embodiment, the column “2p” containing the number of poles 2p, the column “αP” containing the pole pitch angle αP, the column “U2” containing the second odd natural number U2, and the column “αconv” containing a conventional brush nominal separation angle αconv.
The conventional brush nominal separation angle αconv for further corresponding embodiments, that is to say for different two-tuples of the number of poles 2p and the second odd natural number U2, can be calculated as follows: αconv=U2*αP. The conventional brush nominal separation angle αconv is therefore equal to a second product of the pole pitch angle αP of the electrical machine multiplied by the second odd natural number U2. The conventional brush arrangement is based on the idea of associating an integer number of pole pitches αP with one commutation step.
a shows a first angle tolerance range 54 for a brush arrangement according to the invention which does not overlap a second angle tolerance range 56 of a corresponding conventional brush arrangement. In this case, all the brush arrangements α11, α12, α13 within the first angle tolerance range 54 represent a new brush arrangement α11, α12, α13.
A person skilled in the art can use the above design rules, for example with the assistance of a table calculation program, to calculate a table which in each case indicates an angle tolerance range for the first circumferential angle α1 for a multiplicity of tuples of predetermined tolerance angle αT, number of laminates k, number of poles 2p, second odd natural number U2 and pole pitch angle αP. In order to dispense with the attachment of a comprehensive tabular overview, for economic reasons, the following is noted. Particularly for the case of a so-called “random removal”, all the angle tolerance ranges which can be calculated by means of the above design rules are considered to be disclosed not only in their totality, but each individual one of the angle tolerance ranges which can be calculated in this way is also (at least implicitly) considered to have been disclosed in its own right.
The load on the electrical machine may be mechanical, while the drive is electrical (motor operation). Alternatively or additionally, the electrical machine can be driven mechanically, while the load on the electrical machine is electrical (generator operation).
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 003 159.6 | May 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/053589 | 3/19/2010 | WO | 00 | 2/13/2012 |
