DE102009029410A1 - Motor system has brush-commutated electric motor and one or more measurement units, where electric motor has commutator with three brushes, and multiple brushes are provided with similar polarity - Google Patents

Abstract

The motor system (1) has a brush-commutated electric motor (2) and one or more measurement units (9). The electric motor has a commutator (3) with three brushes (4), where multiple brushes are provided with similar polarity. The brushes are connected with a supply potential over a common supply line (6). Independent claims are also included for the following: (1) an apparatus for measuring the rotating speed of an electric motor in a motor system; and (2) a method for measuring the rotating speed of an electric motor in a motor system.

Description

Technical area

The invention relates to brush-commutated DC motors, in which a speed measurement is performed by evaluating a current waveform.

State of the art

A speed of a DC motor is usually with the help of additional position sensors, such. B. Hall sensors, GMR sensors and the like, performed in a known manner. The position sensor is coupled to the rotor of the DC motor, so that a part of the position sensor is also moved during a movement of the rotor. In this case, a current or voltage pulse is generated by the position sensor. The current or voltage pulse is evaluated, z. For example, the pulses are counted during a predetermined time window to obtain an indication of a speed of the DC motor.

Alternative ways to determine the speed sensorless, provide an evaluation of a current ripple on the supply lines of the DC motor. In this case, the current is evaluated on the supply lines, which has a regular waviness in a movement of the rotor of the DC motor due to the groove of the armature and dependent on the movement of the rotor commutation. By irregular patina, mechanical vibrations or circularity on the commutator, the current ripple can be irregular, so that this method of speed measurement is not reliably applicable for all applications.

Furthermore, there is a disadvantage of sensorless speed measurement when used in DC motors with commutators having more than two brushes. In such engine systems, at least two of the brushes are usually supplied with power via a common supply line. As a result, due to the offset of the commutator arrangement of the brushes, the current ripples of the currents are superimposed on the common supply line by the plurality of brushes of the same polarity, are added to the common supply line and weaken due to their phase offset. As a result, the effort in the detection and the evaluation of the current ripples on the supply line in such engine systems is significantly increased, since the sensitivity of the sensorless speed measurement must be selected accordingly.

It is an object of the present invention to provide a motor system with a DC motor, with which an improved determination of the rotational speed can be carried out on the basis of a current profile or by evaluating a current ripple. It is a further object of the present invention to provide a device for determining a rotational speed in an engine system and a method for this purpose.

Disclosure of embodiments.

These objects are achieved by the motor system according to claim 1 and by the device and the method according to the independent claims.

Further advantageous embodiments are specified in the dependent claims.

According to a first aspect, a motor system is provided with a brush-commutated electric motor and with one or more measuring units. The electric motor comprises a commutator with at least three brushes, wherein a plurality of brushes of the same polarity are provided, which are connected via a common supply line to a supply potential, between the supply line and at least one of the plurality of brushes a measuring unit for measuring an indication of a brush current over the corresponding brush is arranged.

An idea of the invention is to provide an engine system with which a determination of a rotational speed of an electric motor can be carried out in an improved manner. By providing the measuring unit for detecting a current between the supply line and one of a plurality of brushes of the same polarity, it is possible to detect current fluctuations due to commutation of the electric motor from interference on the common supply line and to use for determining the speed specification.

Furthermore, the commutator may comprise a number of commutator bars that are contactable with the plurality of brushes, which is not an integer multiple of a pole pair number.

According to one embodiment, the number of commutator bars may correspond to the product increased or decreased by 1 by one pole pair number and one natural number.

Thus, with DC motors having more than one brush per polarity, it can be ensured that the brushes of the same polarity do not commutate simultaneously. This leads to a phase shift between the brush currents, so that on the common supply line to add the current ripples and extinguish due to the non-simultaneous commutation at least partially. This is desirable because the current fluctuations lead to disturbing voltage fluctuations on the DC supply voltage. However, this makes it difficult to detect the frequency of the current ripple, which is an indication of the rotational speed of the electric motor. With the above motor system can detect the individual brush currents, at the same time there is only a small current ripple on the supply line, which corresponds to the sum of several phase-offset brush currents. As a result, the torque ripple can be kept small.

Furthermore, the plurality of brushes may each be assigned a measuring unit. According to one embodiment, the measuring unit may have a measuring resistor or an inductive coupling element.

According to one embodiment, the measuring units may be arranged between the supply line and the plurality of brushes of the same polarity.

It may further be provided that the plurality of brushes have a uniform offset from each other.

In another aspect, an apparatus for measuring a speed indication of an electric motor is provided in the above engine system. The device comprises an evaluation unit which receives at least one detection signal from the one or more measuring units and which is designed to determine the speed indication in dependence on the one or more detection signals.

Furthermore, the evaluation unit can be designed to determine the speed specification as a frequency of the one or more detection signals. Alternatively, the evaluation unit can be designed to determine a difference signal as a difference of a plurality of the detection signals and to determine the speed indication as a frequency of the difference signal.

• – Empfangen des mindestens einen Detektionssignals von der einen oder den mehreren Messeinheiten; und
• – Ermitteln der Drehzahlangabe als eine Frequenz des einen oder der mehreren Detektionssignale oder als eine Frequenz eines Differenzsignals, das einer Differenz von mehreren der Detektionssignale entspricht.

In another aspect, a method of measuring a speed indication of an electric motor is provided in the above engine system. The method comprises the steps:

• - receiving the at least one detection signal from the one or more measuring units; and
• Determining the speed indication as a frequency of the one or more detection signals or as a frequency of a difference signal corresponding to a difference of a plurality of the detection signals.

Brief description of the drawings

Preferred embodiments of the invention are explained below with reference to the accompanying drawings. Show it:

1 a schematic representation of a motor system with a DC motor with four poles and fifteen commutator, which are contacted via two brushes of the same polarity;

2 a schematic representation of a motor system with a DC motor with six rotor poles, twenty commutator and three brushes of the same polarity; and

3 a schematic representation of a motor system with a DC motor with six rotor poles, twenty commutator and two brushes one polarity and a brush of a different polarity.

Like reference numerals designate elements of equal or comparable function.

Description of embodiments

In 1 is an engine system 1 shown schematically. The engine system 1 includes a DC motor 2 who is a commutator 3 on a runner 12 having. The runner 12 has rotor windings 11 on, electrically via commutator bars 13 of the commutator 3 can be contacted. The commutator bars 13 be by brushing 4 electrically contacted, with the brushes 4 during a rotation of the rotor 12 on the commutator blades 13 along and thereby each with one or two of the commutator bars 13 to create an electrical connection. The on the brushes 4 applied voltage is then at the contacted commutator 13 associated rotor windings 11 at.

The DC motor 2 has four rotor poles 14 ie, two pole pairs, each of which may be formed as a permanent magnet to provide a field magnetic field. Usually, a number of brushes 4 for the commutator 3 provided, with two brushes each 4 have the same polarity. The brushes 4 are in this Embodiment around the commutator 3 arranged evenly distributed, ie the brushes 4 are offset by 90 ° around the commutator 3 arranged and adjacent brushes have different polarities.

The number of commutator bars 13 is in the embodiment of 1 on 15 set so that the offset by 90 ° around the commutator brushes 4 at different times with the next commutator blade 5 come into contact to make an electrical connection with the next commutator 5 associated rotor winding 11 to obtain. The brushes 4 are of the same polarity by an electrical connection with each other and with an associated supply line 6 connected. About the supply lines 6 a supply voltage is provided, thus each between two brushes 4 different polarity is applied. On the supply line 6 that with the brushes 4 Thus, a sum current flows as the sum of brush currents passing through the brush 4 of the same polarity flow.

Due to the odd number of commutator bars 13 the rotor windings are arranged in the form of a loop winding, wherein each of the rotor windings 11 by adjacent commutator bars 13 will be contacted.

In the on the supply lines 6 flowing cumulative current through the two brushes 4 of a brush pair is the fundamental of the brush currents ( 15 , Order of the rotational frequency) eliminated by superposition of the brush currents. Only the first harmonic with significantly lower amplitude remains on the supply line 6 , However, the signal of the first harmonic is much lower than that of the fundamental and therefore difficult to detect. In order to have a sufficiently large current signal available, it is therefore proposed to provide a corresponding measuring device, the current flow through one or both of the brushes 4 evaluates the same polarity.

In the engine system of 1 are the brushes subjected to the positive supply potential 4 each via a measuring resistor 9 with the supply line 6 connected for the high supply potential, so that flows through the respective measuring resistor only the brush current as a partial flow. Of course, alternatively or additionally, measuring resistors could also be applied to the brushes 4 be connected for the low supply potential. At the measuring resistors 9 falls according to the brush current in each case a measurement voltage as a detection signal from the qualitatively in the voltage-time diagrams of the measuring resistors 9 is indicated. The evaluation of the current ripple measured there can be carried out with the aid of an evaluation unit 10 done with the measuring resistors 9 is connected to detect the applied there measuring voltage as an indication of the respective brush current.

For this purpose, the corresponding detection signal can be evaluated, the one of the brushes 4 assigned. This will be the evaluation unit 10 provided a signal in which the fundamental wave of the brush currents is not eliminated by superposition, so that from the corresponding detection signal in a simple manner, the rotational speed can be detected.

The evaluation can be based on one of the detection signals as well as with the aid of several detection signals for a plurality of brushes 4 respectively. In this case, the evaluation can be carried out separately and the obtained rotational speed inputs, which are substantially proportional to the frequency of the detection signal, are made plausible together.

Alternatively or additionally, a difference of the detection signals can be made to obtain a difference signal. The difference can be in the evaluation unit 10 z. B. by means of a differential amplifier (not shown) and the like. In the illustrated embodiment, the information about the brush currents to each other at the commutator as detection signals 3 opposite brushes 4 detected, which have a phase offset of 180 ° to each other. Thus, a doubling of the amplitude of the difference signal to be evaluated is achieved in the difference formation. This simplifies the evaluation in the evaluation unit 10 considerably.

2 shows a schematic representation of an engine system 1 with a DC motor 2 in which the DC motor 2 six rotor poles 14 with 20 commutator bars 13 having. The 20 commutator bars 13 be over three brushes 4 positive polarity and three brushes 4 contacted negative polarity. The three brushes 4 Negative polarity are phase-shifted by 120 °. The brushes of positive polarity 4 are each 60 ° to the brushes 4 out of phase with negative polarity. In other words the brushes 4 have an offset of 60 ° to each other, with adjacent brushes 4 have different polarities. The measuring units in the form of measuring resistors 9 are each between the supply line 6 and the brushes 4 arranged negative polarity.

In total current through all brushes 4 Negative polarity eliminates the fundamental wave of the brush currents (the 20th order of the rotational frequency). As a result, remains on the corresponding supply line 6 on which brush flows through the brushes 4 add negative polarity, obtained via the second harmonic (60th order of the rotational frequency) with significantly lower amplitude.

In the embodiment shown the 2 the brush currents are passed through all the brushes of negative polarity with the help of the measuring resistors 9 detected, and corresponding detection signals are the evaluation 10 fed. There, the speed can be determined as described above by a frequency measurement on one of the detection signals or based on a difference between a plurality of the detection signals, since the detection signals due to the phase shift of the commutation of the commutator 13 through the brushes 4 out of phase.

In 3 is another embodiment of an engine system 1 with a DC motor 2 shown in which the DC motor 2 six rotor poles and 20 commutator bars 13 having. The 20 commutator bars 13 be over two brushes 4 positive polarity and a brush of negative polarity contacted. The two positive polarity brushes are positioned at 120 ° out of phase with the commutator, while the negative polarity brush is offset by 60 ° with one of the positive polarity brushes, preferably positioned between the positive polarity brushes. While in the summation current on the supply line 6 for both brushes 4 positive polarity, the fundamental of the brush currents (20th order of the rotational frequency) is reduced by the phase offset, if only one measuring unit, ie here a measuring resistor 9 in a feed branch for a brush 4 positive polarity is provided, the power loss can be reduced, since only about half of the total supply current must be passed through the measuring unit.

The measuring unit is preferably designed as a measuring resistor, so that the current flowing thereby can be tapped in the form of a detection voltage. Alternative ways to measure the current are also possible, such. As the measurement of the alternating component of the current through inductive coupling and the like, which also has the advantage that a DC component of the supply current not to the evaluation unit 10 arrives. Alternative to the measuring resistor 9 can also be a simple trace for supplying the current to the respective brushes 4 be provided, wherein a voltage drop over a portion of the conductor is provided as a detection signal of the evaluation unit.

To realize the invention is essential that several brushes 4 are provided of the same polarity, to which the supply voltage potential of the supply voltage is supplied via corresponding partial supply lines. The DC motors described herein 2 have a number of pole pairs which is greater than 1, since otherwise the provision of several brushes of the same polarity is not meaningful.

To allow for the commutation of a respective next Kommutatorlamelle 13 at one of the brushes, a phase offset between the brushes, which are provided with the measuring units, occurs, the number of commutator is as possible no integer multiple of the number of pole pairs. This can be done, for example, by complying with the condition L = j × p +/- 1 can be achieved, where L is the number of commutator bars 13 , p is the number of pole pairs and j is a natural integer.

Claims (11)

Engine system ( 1 ) with a brush-commutated electric motor and with one or more measuring units ( 9 ), wherein the electric motor ( 2 ) a commutator ( 3 ) with at least three brushes ( 4 ), wherein at least a plurality of brushes ( 4 ) of the same polarity, which are connected via a common supply line ( 6 ) are connected to a supply potential, wherein between the supply line ( 6 ) and at least one of the plurality of brushes a measuring unit ( 9 ) for measuring an indication of a brush current via the corresponding brush ( 4 ) is arranged. Engine system ( 1 ) according to claim 1, wherein the commutator comprises a number of commutator bars ( 13 ) associated with the plurality of brushes ( 4 ) are contactable, which is not an integer multiple of a pole pair number. Engine system ( 1 ) according to claim 2, wherein the number of commutator bars ( 13 ) corresponds to the increased or reduced by 1 product of a Polpaarzahl and a natural number. Engine system ( 1 ) according to one of claims 1 to 3, wherein a plurality of brushes each have a measuring unit ( 9 ) assigned. Engine system ( 1 ) according to one of claims 1 to 4, wherein the measuring unit ( 9 ) has a measuring resistor or an inductive coupling element. Engine system ( 1 ) according to one of claims 1 to 5, wherein the measuring units between the Supply line ( 6 ) and the multiple brushes ( 4 ) of the same polarity are arranged. Engine system ( 1 ) according to one of claims 1 to 6, wherein the plurality of brushes ( 4 ) have a uniform offset from each other. Device for measuring a speed specification of an electric motor ( 2 ) in an engine system ( 1 ) according to one of the preceding claims, with an evaluation unit ( 10 ) containing at least one detection signal from the one or more measuring units ( 9 ) and configured to determine the speed indication in response to the one or more detection signals. Apparatus according to claim 8, wherein the evaluation unit ( 10 ) is configured to determine the speed indication as a frequency of the one or more detection signals. Apparatus according to claim 8, wherein the evaluation unit ( 10 ) is configured to determine a difference signal as a difference of a plurality of the detection signals and to determine the speed indication as a frequency of the difference signal. Method for measuring a speed specification of an electric motor ( 2 ) in an engine system ( 1 ) according to one of the preceding claims, comprising the steps of: - receiving the at least one detection signal from the one or more measuring units; Determining the speed indication as a frequency of the one or more detection signals or as a frequency of a difference signal corresponding to a difference of a plurality of the detection signals.

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