EP3533115A1

EP3533115A1 - Wear-monitoring device of a brush of a current-transferring device in an electric machine

Info

Publication number: EP3533115A1
Application number: EP17800716.7A
Authority: EP
Inventors: Istvan DEAK
Original assignee: Robert Bosch GmbH; SEG Automotive Germany GmbH
Current assignee: Robert Bosch GmbH; SEG Automotive Germany GmbH
Priority date: 2016-10-27
Filing date: 2017-10-27
Publication date: 2019-09-04
Also published as: DE102016221226A1; US20200182935A1; CN109891687A; WO2018078085A1

Abstract

The invention relates to a wear-monitoring device of a brush of a current-transferring device in an electric machine comprising a measuring element, which is arranged at a distance from the brush and forms an electrical capacitor together with the brush, the capacitance of which electrical capacitor depends on the position of the brush relative to the measuring element.

Description

description

title

Wear monitoring device of a brush of a

Power transmission device in an electrical machine

The invention relates to a wear monitoring device of a brush of a power transmission device in an electric machine according to the preamble of claim 1. Prior art

Power transmission devices such as commutation devices in electrical machines are used to transmit power to the armature of the electric machine and include brushes in brush holders, which are supplied with power via strands. The brushes are from a

Brush spring pressed radially against the lateral surface of a circulating with the armature collector. Due to the frictional contact with the collector shell surface, the brushes are subject to wear and tear

Wear monitoring device can be detected.

From DE 197 55 232 AI a wear monitoring device is known which comprises a signal generator on the carbon brush, which upon reaching a predetermined wear limit of the brush against an electric

Bending contact is moved, which is part of a signal circuit. This will trigger a signal indicating that the wear limit has been reached

is pointed out.

From DE 10 2013 204 426 AI a wear monitoring device is known in which the current position of a permanently connected to the brush Conductor is detected, being closed from the position of the conductor on the wear of the brush.

Disclosure of the invention

The wear monitoring device according to the invention is for

Monitoring the wear of a brush of a power transmission device used in an electrical machine. The brush is in one

Brush holder slidably received and is due to the force of a spring element on the lateral surface of an armature-side, current-carrying

Component of the electric machine pressed, over the current to one

Armature winding is transmitted. The power supply of the brush via a conductor, which is either connected to a power source or electrically grounded.

The current transmission device is, for example, a commutation device with an armature-side collector for

Power transmission and turning, on the cylindrical surface of the brush rests, which is pressed by the spring element radially against the lateral surface of the collector. The collector has collector fins, which with the

Armature windings are electrically connected. such

Commutation devices are preferably used in DC motors. The power transmission device can also, according to an alternative

Execution be designed as a slip ring system in a slip ring rotor machine. Current is transferred to an armature winding via an armature-side slip ring against which the brush rests. The slip ring rotor machine is a three-phase asynchronous machine which is used, for example, as a generator.

Due to the frictional contact between the end face of the brush holder slidably received in the brush holder and the circumferential, armature-side component, the brush is subjected to permanent wear. With the wear monitoring device according to the invention, the wear can monitored the brush and in particular a critical wear limit can be detected.

The wear monitoring device comprises a current-conducting measuring element assigned to the brush, whose electrical voltage depends on the position of the brush in the brush holder. The position of the brush changes in the

Brush holder, so also changes the electrical voltage of the current-conducting measuring element, which by means of an electrical measuring device of the

Wear monitoring device can be detected.

The electrical measuring element is arranged at a distance from the brush and together with the brush forms an electrical capacitor whose electrical capacitance depends on the relative position of the brush to the measuring element. The brush and the measuring element thus each form capacitor halves, between which an electric field is produced due to an energization of the brush and, consequently, a voltage potential in the measuring element which can be detected by means of the measuring device.

This embodiment has the advantage that a non-contact, capacitive measurement is performed and no contact between the measuring element and the brush is required. The measuring element is at a distance to the brush, there is no contact between the measuring element and the brush. Accordingly, there is also no contamination or corrosion of the measuring element, whereby the function of the wear monitoring device could be impaired.

According to a preferred embodiment, the measuring element is fixed to the housing and can not perform any relative movement with respect to the housing. During wear, the length of the brush and thus also the relative position of the brush relative to the measuring element changes, which changes the capacitance of the electrical capacitor, consisting of brush and measuring element, which leads to a correspondingly changed electrical voltage in the measuring element Measuring device can be determined.

The measuring element is either on a housing component of

Power transmission device arranged or, according to a preferred Execution, in or on a brush holder, in which the brush is displaceably guided and which advantageously also receives the spring element which acts on the brush against the lateral surface of the collector. For example, the measuring element may be integrated in the wall of the brush holder, which consists of an electrically non-conductive material. This embodiment has the advantage that the measuring element is in the immediate vicinity of the brush and thus can form a significant electric field between the measuring element and the brush, without the risk of an immediate, a short circuit

causing contact between the measuring element and the brush.

According to a further advantageous embodiment, the brush in the

Unused condition at least 50% of the surface of the measuring element on. It may be appropriate if the surface of the brush in the

unused condition at least 90%, for example 95% of

facing surface of the measuring member has, based on the mutually facing and opposite side surfaces of measuring member and brush. In the unconsumed initial state, the measuring element and the brush are advantageously located opposite one another in order to achieve a comparatively high capacitance of the capacitor. Accordingly, the brush and measuring element have a high degree of coverage in the initial state of the brush. During the wear of the brush, this changes its relative position relative to the measuring element, whereby the surface portion of the brush opposite the measuring element decreases and the capacitance of the capacitor changes.

According to a further expedient embodiment, the measuring member surrounds the brush partially or completely. Thus, it may be expedient, for example, to integrate the measuring element into the brush holder, which preferably has a rectangular cross-sectional geometry for receiving the brush, the measuring element in or on exactly one side of the brush holder, on two sides, on three sides or on four sides to arrange. When positioned on all four sides of the measuring member surrounds the inner brush completely, whereas when positioned on two or three sides of the measuring member surrounds the brush only partially and when positioned on one side only the measuring member of the brush. Conveniently, the measuring element is in the Wall of the brush holder integrated, so that a direct contact between the brush and the measuring member is prevented.

The measuring element is designed, for example, as a current plate, which lies opposite the brush and in particular is arranged parallel to the brush. In a partial or complete encompassing each other in the various walls of the brush holder each current plates are integrated, which are interconnected and together form the measuring element.

According to yet another expedient embodiment, the

Wear monitoring device on a drive circuit for generating an excitation voltage in the brush. Via the drive circuit, an exciter voltage signal is generated in the brush, wherein due to the capacitive coupling of the brush to the measuring element also in the measuring element a

corresponding voltage curve sets that via the electrical

Measuring device, which advantageously also for

Wear monitoring device heard, can be determined. When

Exciter voltage signal, for example, a PWM-shaped

Excitation voltage (pulse width modulation) with a rectangular

Voltage generated, which also sets in the measuring element.

The electrical connection between the measuring element and one as

Transmitter running measuring device, for example, via a stamped grid. The drive circuit is designed, for example, as a field regulator, which comprises a transistor, for example a MOSFET or an H-bridge, wherein via the drive circuit a defined

Voltage signal is applied to the brush.

The measured voltage in the measuring element can be compared to

Operating voltage can be set, with which the brush is energized for energizing the armature winding.

According to a further expedient embodiment, the operating voltage is used as excitation voltage. The adjusting in the measuring element voltage is in a known ratio to the operating voltage in the brush, wherein when a wear of the brush, a voltage change in the measuring element, caused by a change in capacity, sets.

Further advantages and expedient embodiments can be taken from the further claims, the description of the figures and the drawings. Show it:

1 is a schematic representation of a brush in a brush holder of a power transmission device in an electrical machine, shown in the unconsumed initial state and in a state of wear, each with an associated measuring element,

Fig. 2 shows the course of an excitation voltage and the course of the voltage in the measuring element in response to the excitation voltage, shown in FIG

Initial state and in the state of wear of the brush,

1 shows corresponding illustrations of the brush in the initial state and with wear, but with three associated measuring members on the brush holder,

Fig. 4 Fig. 2 corresponding representations of the excitation voltage and the

Response voltage in the first measuring element,

Fig. 5 to 8

in cross section a brush in a brush holder with different embodiments of a measuring element,

9 shows a drive circuit for generating an excitation voltage.

In the figures, the same components are provided with the same reference numerals.

In Fig. 1 is in two different states of wear, a brush 1 in a brush holder 2 of a power transmission device in an electrical

Machine shown. Using the power transmission device

Armature windings energized. The current transmission device is, for example, a commutation device with one with the armature circulating collector 3, on the lateral surface of the brush 1 is applied. The brush 1 is slidably mounted in the brush holder 2 and is of a

Spring element 4, which is supported on the bottom of the brush holder 2, pressed against the lateral surface of the collector 3. Due to the frictional contact between the end face of the brush 1 and the lateral surface of the collector 3 is subject to

Brush a wear. In Fig. 1, the brush is in the upper picture in

Unused initial state shown in the lower picture, the brush shown in the wear state, in which the brush length compared to the

Unused condition is reduced. The brush 1 is energized via a current conductor 5.

In order to be able to detect the current state of wear and if necessary to generate a warning signal when a wear limit is reached, the

Power transmission device provided with a wear monitoring device comprising a current-conducting measuring element 6, which is associated with the brush 1. The measuring element 6 is formed for example as a current conductor or as an electrically conductive plate and spaced from the brush 1, but arranged parallel to this. The measuring element 6 lies, for example, in the wall of the brush holder 2. In any case, direct contact between the brush 1 and the measuring element 6 is excluded.

The brush 1 and the current-conducting measuring element 6 each form

Capacitor halves and together an electric capacitor whose capacity depends on the relative position between brush 1 and measuring element 6. The measuring element 6 is fixed to the housing, in particular fixed to the

Brush holder 2 connected, in particular integrated in the wall of the brush holder 2. With increasing wear, the length of the brush 1 is shortened, as a result of which the relative position between the brush 1 and the measuring member 6 also changes. As a result, a changing capacitance of the capacitor with the capacitor halves of the brush 1 and the measuring element 6 is established.

The change in the capacitance of the capacitor with brush 1 and measuring element 6 can be detected via the electrical voltage potential Ui of the measuring element 6. Between the brush 1 and the measuring element 6, an electric field E is generated, which generates the voltage potential Ui in the measuring element 6. The voltage Ui of the brush 6 can be determined by means of an electrical measuring device. Upon a change in the voltage Ui, triggered by a change in capacitance due to a wear-related shortening and change in position of the brush 1, a warning signal can be generated as soon as the voltage Ui of the measuring element 6 reaches a threshold value.

The measuring element 6 is arranged axially at a distance from the open end side of the brush holder or to the collector 3. In the unconsumed initial state of the brush 1, this has a greater length than the measuring element 6 and is arranged opposite the measuring element 6 in such a way that the brush 1 extends completely in the height of the measuring element 6. Im consumed

On the other hand, the state of wear according to the lower picture in FIG. 1 is shifted so far in the direction of the collector 3 due to the wear that there is only a partial overlap between the brush 1 and the measuring element 6, which results in a lower electrical capacitance.

In the exemplary embodiment according to FIG. 1, the electrical measuring device comprises precisely one measuring element 6, which is fixed to the housing or arranged on the brush holder 2. In FIG. 2, voltage curves U for a field voltage U _er r (upper picture) and a measuring element voltage Ui (lower picture) are shown in a time-dependent manner. The excitation voltage U _er r is applied to the brush 1, for example by means of a drive circuit as shown in Fig. 9. The exciter voltage U _er r is formed as a rectangular PWM signal (pulse width modulation), which leads to the exciting current waveform I _err shown in the upper graph. Due to the capacitive coupling between brush 1, which is acted upon by the excitation voltage Uerr, and the measuring element 6, the measuring element voltage Ui adjusts according to the lower diagram. Shown in the lower diagram is the measuring element voltage UI, A for the unconsumed initial state of the brush 1 and the measuring element voltage Ui.β for a brush, which according to FIG. 1, lower image is reduced by wear. In the unconsumed initial state, the sensor voltage UI, A is higher than in the used state according to

Transducer voltage UI, B. This difference can be detected via the measuring device, wherein the warning signal is generated as soon as the

Transducer voltage drops below a threshold. In Fig. 3, a variant with a plurality, in particular three superposed, electrically conductive measuring members 6 is shown, each forming a condenser with the brush 1. Each capacitor, consisting of brush 1 and one of the measuring elements 6, has a certain capacity, which, however, depends on the relative position of the brush 1 in the brush holder 2 and opposite each measuring element 6.

Shown in Fig. 4 in the upper graph, the exciter voltage U _er r and the exciting current \ _e ", which are identical to the excitation voltage and the

Excitation current as shown in FIG. 2. The excitation voltage U _er r is present as a rectangular PWM signal.

In Fig. 4, lower graph is the Meßgliedspannung Ui for the first

Measuring member shown. The voltages of the other measuring elements are designated U2 and U3. As can be seen from the diagram, the measuring element voltage Ui.A is provided with a high amplitude in the uncut initial state, whereas in the worn state of the brush 1, in which it has a shortened length, the measuring element voltage UI, B drops to zero. According to FIG. 3, the lower image, the brush 1 is shortened so far that there is no longer any overlap to the upper measuring element 6, so that, correspondingly, the electrical capacitance drops to zero and the measuring element voltage UI, B also lies at zero. This complete drop to zero can be ascertained, as well as for the second measuring element with the measuring element voltage U2 and the third measuring element with the measuring element voltage U3. A warning signal is generated, for example, as soon as the measuring element voltage I 1 or the measuring element voltage U 3 drops to zero.

FIGS. 5 to 8 show different embodiments of the measuring element 6. All embodiments have in common that the measuring element 6 is completely integrated into the wall of the brush holder 2 and thus there is no contact with the brush 1 contact.

According to FIG. 5, the measuring element 6 extends in the form of a plate only on one side of the brush holder 2 and faces the brush 1. In Fig. 6, the measuring member 6 is formed angularly and is opposite to the measuring member 1 on two sides. In Fig. 7, the measuring member 6 is U-shaped and is located on three sides of the brush 1 opposite. In Fig. 8, the measuring member 6 is circumferentially rectangular in shape and completely surrounds the brush 1, so that the measuring member 6 is opposite to all sides of the brush 1.

In Fig. 9, a drive circuit 7 for generating an excitation voltage U _{err is shown} in the brush. The drive circuit 7 comprises a transistor 8, for example a MOSFET whose drain terminal 8a is connected to the voltage B + of a voltage source 9, whereas the source terminal 8b of the transistor via a brush with the positive terminal F + a Läufererbzw. Armature winding is connected. The negative terminal F- of the armature winding is connected via another brush to the ground GND. Parallel to

Armature winding is connected in the reverse direction of a freewheeling diode 10. Of the

Transistor is driven by a clocked signal, via the

Duty cycle of this signal, the height of the excitation current or the

Can set excitation voltage.

Optionally, the drive circuit 7 can also be equipped with an H-bridge, which enables further functions in the exciter circuit.

Claims

claims

1 . Wear monitoring device of a brush (1) of a

Power transmission device in an electrical machine, in which the wear of the brush (1) in dependence on the position of the brush (1) in a brush holder (2) can be determined with one of the brush (1)

associated, current-conducting measuring member (6) whose electrical voltage from the position of the brush (1) in the brush holder (2) depends, characterized in that the measuring member (6) is arranged at a distance from the brush (1) and together with the brush ( 1) an electrical

Capacitor forms whose electrical capacitance depends on the relative position of the brush (1) to the measuring element (6).

2. Wear monitoring device according to claim 1, characterized

in that the measuring element (6) is fixedly arranged in or on a brush holder (2) in which the brush (1) is displaceably guided.

3. Wear monitoring device according to claim 2, characterized

in that the measuring element (6) is integrated in the wall of the brush holder (2).

4. Wear monitoring device according to one of claims 1 to 3, characterized in that the measuring member (6) surrounds the brush (1) partially or completely.

5. wear monitoring device according to one of claims 1 to 4, characterized in that the measuring member (6) is designed as a current plate, the brush (1) opposite, in particular parallel

is arranged opposite.

6. Wear monitoring device according to one of claims 1 to 5, characterized in that in the unconsumed state, the brush (1) at least 50%, in particular at least 90% of the area of the

Measuring member (6).

7. Wear monitoring device according to one of claims 1 to 6, characterized in that the current transmission device is designed as a commutation device.

8. Wear monitoring device according to one of claims 1 to 7, characterized in that the current transmission device is designed as a slip ring system in a slip ring rotor machine.

9. Wear monitoring device according to one of claims 1 to 8, with a drive circuit (7) for generating an excitation voltage in the brush (1).

10. A method for operating a wear monitoring device according to claim 9, wherein in the drive circuit (7), a PWM-shaped excitation voltage is generated.

1 1. Power transmission device with a wear monitoring device according to one of claims 1 to 9.

12. Electric machine with a power transmission device according to

Claim 1 1.