METHOD FOR DETERMINING A STATE OF AN ELECTRIC MOTOR AND A CORRESPONDING ELECTRIC MOTOR AND FAN

Abstract

A method for determining a state of an electric motor having a stator (2) and a rotor (3) rotatably mounted relative to the stator (2) is disclosed. Due to a rotary motion of the rotor (3), a pressure difference (p) relative to an environment (15) of the electric motor (1, 1′, 1″, 1′″) is caused in an air space (16) inside the electric motor (1, 1′, 1″, 1′″). Here, in a normal state of the electric motor (1, 1′, 1″, 1′″), the pressure difference depends on an actual rotational speed (n) of the rotor (3). A corresponding electric motor suitable for carrying out this method is disclosed, wherein the electric motor may be part of a fan.

Claims

1. Method for determining a state of an electric motor which has a stator (2) and a rotor (3) mounted rotatably relative to the stator (2), wherein due to a rotational movement of the rotor (3) in an air space (16) inside the electric motor (1, 1′, 1″, 1′″) a pressure difference (p) relative to an environment (15) of the electric motor (1, 1′, 1″, 1′″) is caused, wherein in a normal state of the electric motor (1, 1′, 1″, 1′″) the pressure difference is dependent on an actual rotational speed (n) of the rotor (3), comprising the steps: determining an actual pressure difference (p) between the air space (16) and an environment (15) of the electric motor (1, 1′, 1″, 1′″), determining the actual rotational speed (n) of the rotor (3), and calculating a parameter (k) based on the actual pressure difference (p) and the actual rotational speed (n), resulting in a parameter (k) representative of the state of the electric motor.

2. The method according to claim 1, wherein the parameter (k) is compared with a threshold value and in that a state of the electric motor (1, 1′, 1″, 1′″) is determined based on a result of the comparison of the parameter (k) with the threshold value.

3. The method according to claim 1, wherein the parameter (k) is calculated as a quotient of the actual pressure difference (p) and a square of the actual rotational speed (n).

4. The method according to claim 1, wherein the parameter (k) is standardized to a reference value, wherein the reference value is determined during initial commissioning of the electric motor or during a final test after production of the electric motor.

5. The method according to claim 1, wherein the actual pressure difference (p) is determined based on pressure values (p) which are measured by means of an absolute pressure sensor (21, 27) for the air space (16) at different actual rotational speeds, wherein a first measurement is carried out when the electric motor (1, 1′″) is at a standstill and a second measurement is carried out at an actual rotational speed not equal to 0.

6. The method according to claim 1, wherein the actual pressure difference (p) is measured by means of two absolute pressure sensors, wherein a first absolute pressure sensor (21, 27) is subjected to a pressure in the air space (16) and a second absolute pressure sensor measures an air pressure representative of the pressure in the environment of the electric motor.

7. The method according to claim 1, wherein the actual pressure difference (p) is measured by means of a differential pressure sensor (22, 31), wherein a first sensor surface of the differential pressure sensor (22, 31) is subjected to a pressure in the air space and a second sensor surface of the differential pressure sensor (22) is subjected to a pressure in the environment (15) of the electric motor (1′, 1″, 1′″).

8. The method according to claim 1, wherein the determined state of the electric motor (1, 1′, 1″, 1′″) describes a contamination of the electric motor (1, 1′, 1″, 1′″) or a leakage of the electric motor (1, 1′, 1″, 1′″).

9. The method according to claim 1, wherein, when determining the actual pressure difference over a measurement period, a plurality of pressure differences are determined, and the actual pressure difference is calculated from the plurality of pressure differences by averaging.

10. An electric motor, with a stator (2), a rotor (3) mounted rotatably relative to the stator (2) and an air space (16) formed inside the electric motor, wherein in a normal state of the electric motor (1, 1′, 1″, 1′″), the rotor (3), due to its rotational movement, causes a pressure difference in the air space (16) with respect to an environment (15) of the electric motor (1, 1′, 1″, 1′″), wherein the electric motor (1, 1′, 1″, 1′″) additionally comprises: a pressure sensor system, a rotational speed determination system and an evaluation unit (24), wherein the pressure sensor system is designed for determining an actual pressure difference between an environment (15) of the electric motor (1, 1′, 1″, 1′″) and the air space (16), wherein the rotational speed determination system is designed to determine an actual rotational speed (n) of the rotor (3), and wherein the evaluation unit (29) is designed to determine a state of the electric motor (1, 1′, 1″, 1′″) on the basis of the actual pressure difference and the actual rotational speed.

11. An electric motor according to claim 10, further comprising a cooling wheel (11) is coupled to the rotor (3), wherein the cooling wheel (11) causes the pressure difference in the air space (16).

12. An electric motor according to claim 10, further comprising an air outlet (13), with stator rotor ribs or a labyrinth gap, wherein a degree of contamination of the air outlet (13) influences the actual pressure difference in the air space (16).

13. An electric motor according to claim 10, wherein the pressure sensor system is formed by an absolute pressure sensor (21, 27) with a rotational speed-based calculation unit, two absolute pressure sensors or a differential pressure sensor (22, 31).

14. An electric motor according to claim 10, wherein the air space (16) is formed in an electronics housing (5) formed in or on the electric motor (1, 1′, 1″, 1′″), wherein the electronics housing (5) preferably is formed on a stator bushing (4) of the electric motor (1, 1′, 1″, 1′″).

15. An electric motor according to claim 10, wherein the electric motor (1, 1′, 1″, 1′″) is an EC motor (Electronically Commutated Motor) or an external rotor motor.

16. An electric motor according to claim 10, further comprising a communication unit which is designed to send state information obtained by means of an evaluation unit (29) to a management unit.

17. An electric motor according to claim 16, further comprising a memory (30), wherein state information, parameters, or further variables derived therefrom are stored in the memory (30) by means of the evaluation unit (29).

18. An electric motor according to claim 10, wherein the rotor (3) of the electric motor (1, 1′, 1″, 1′″) is coupled to an impeller of a fan.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0045] FIG. 1 a section of a first exemplary embodiment of an electric motor in external rotor design according to the disclosure with an absolute pressure sensor arranged in an electronics housing,

[0046] FIG. 2 the section according to FIG. 1 with additional arrows drawn in to illustrate air movements,

[0047] FIG. 3 a diagram of a pressure difference as a function of rotational speed for different states of an electric motor,

[0048] FIG. 4 a section of a second exemplary embodiment of an electric motor in external rotor design according to the disclosure with a differential pressure sensor in a first embodiment,

[0049] FIG. 5 a section of a third exemplary embodiment of an electric motor according to the disclosure in external rotor design with a differential pressure sensor in a second embodiment,

[0050] FIG. 6 a section of a fourth exemplary embodiment of an electric motor in external rotor design according to the disclosure with a pressure sensor arranged outside the electric motor via a pressure line,

[0051] FIG. 7 a section through a modification of the exemplary embodiment according to FIG. 6 with an external differential pressure sensor,

[0052] FIG. 8 a block diagram showing basic functional elements of a circuit for implementing an exemplary embodiment of the method according to the disclosure,

[0053] FIG. 9 a diagram showing an example of a time curve of a parameter characterizing a state of the electric motor, and

[0054] FIG. 10 is a diagram with another example of a time curve of a parameter.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0055] FIG. 1 shows a section of a first exemplary embodiment of an electric motor according to the disclosure, which is in external rotor design. For the sake of clarity, some parts are omitted that are not important for understanding the disclosure, for example the winding packages for the stator and rotor and most of the motor electronics. The electric motor 1 comprises a stator 2 and a rotor 3, which—as already mentioned—are only indicated. The stator 2 is arranged around a stator bushing 4. An electronics housing 5 is formed on the stator bushing 4, in which motor electronics 6 are arranged (only indicated in FIG. 1) and which is closed with an end cover 7. The rotor 3 is mounted for rotation around a motor axis 8 by means of two bearings 9, 10. A cooling wheel 11 is coupled to the rotor 3, which conveys air through the electric motor 1. A motor housing 12 encloses the electric motor and is inserted in a labyrinth gap which is thereby created at the stator bushing 4.

[0056] FIG. 2 shows how the air will move when the rotor 3 rotates. The cooling wheel 11 conveys air through the electric motor 1, wherein the air leaves the motor housing 12 at the area 13 which is rotationally symmetrical with respect to the motor axis 8. Among other things, the rotary motion of the cooling wheel 11 causes air to be drawn from the electronics housing through a bearing tube 14 formed in the stator bushing and conveyed to the area 13. Since the end cover 7 seals the electronics housing 5 from the environment 15, a pressure difference is created in the electronics housing 5, in this case a negative pressure. This negative pressure depends on the rotational speed n of the rotor. The greater the rotational speed, the greater the negative pressure. This negative pressure depends on how unhindered by ventilation effects air can be moved in the electric motor 1 and how unhindered the air can leave the electric motor 1 at area 13. Thus, an air space 16 is formed in the electronics housing 5 in accordance with an embodiment.

[0057] FIG. 3 shows exemplary curves for the negative pressure in the air space 16 as a function of the rotational speed. The topmost curve 17 (solid line) shows the pressure curve with a clean engine. This means that here no or little dirt affects ventilation effects within the electric motor. This state is also referred to here as the “normal state”. This curve can be measured, for example, during initial commissioning or during final testing of an electric motor. The second curve 18 (dashed line) shows a dirty engine, the third curve 19 (dashed line) shows a heavily dirty engine. It can be seen that the pressure difference becomes smaller and smaller as a function of rotational speed, the more dirt affects the ventilation effects. Curve 20 (dotted line) shows another state in which the end cover 7 does not sufficiently cover the air space. As a result, the negative pressure created by the ventilation effects can be immediately compensated by air flowing in. It can be seen that the negative pressure practically cannot form even with increasing rotational speed. This can be used to conclude that the engine is sucking “false air”.

[0058] To determine the pressure in the air space 16, an absolute pressure sensor 21 is arranged in the air space 16 to measure the air pressure in the air space. In the embodiment example according to FIG. 1, this pressure sensor 21 is arranged on the circuit board of the motor electronics 6. The actual pressure difference between air space 16 and environment 15 is detected by the fact that the air pressure of environment 15 is present in air space 16 at a rotational speed n=0 revolutions/min at a time t.sub.1. At a measuring time t.sub.2 at a rotational speed n≠0 revolutions/min, the same absolute pressure sensor 21 measures the pressure inside the electronics housing. In this way, the actual pressure difference can be calculated from the two measured pressure values at time t.sub.1 and at time t.sub.2.

[0059] FIG. 4 shows a second embodiment of an electric motor 1′ according to the disclosure. This embodiment example is similar in large parts to the first embodiment example, although a differential pressure sensor 22 is now used instead of the absolute pressure sensor 21. The differential pressure sensor 22 includes a first connection 23 and a second connection 24. The first connection 23 directs a pressure input thereto to a first sensor surface, while the second connection 24 directs a pressure input thereto to a second sensor surface. The differential pressure sensor 22 measures the pressure difference between the first sensor surface and the second sensor surface, and thus between the pressure input to the first connection 23 and the pressure input to the second connection 24. In this embodiment, the first connection 23 is pressurized with the air pressure in the air space 16. The second connection 24 is pressurized with an air pressure of the environment 15 via a pressure line 25 and a feedthrough 26.

[0060] In this way, the differential pressure sensor 22 can directly measure the actual pressure difference between the air space 16 and the environment 15 without the need for a rotational speed change. However, the rotational speed must then be unequal to 0 revolutions/minute.

[0061] FIG. 5 shows a third exemplary embodiment of an electric motor 1″ according to the disclosure, which also uses a differential pressure sensor 22. The first connection 23 of the differential pressure sensor 22 is again subjected to an air pressure in the air space 16. The second connection 24 is arranged on the side of the differential pressure sensor 22 facing the stator bushing 4 and is contacted through the stator bushing 4 into the rotor space. Also in this exemplary embodiment, the differential pressure sensor 22 can determine an actual pressure difference that is dependent on the degree of contamination on the cooling wheel 11 and/or on the area 13.

[0062] FIG. 6 shows a fourth exemplary embodiment of an electric motor 1′″ according to the disclosure. This exemplary embodiment is broadly similar to the other exemplary embodiments. However, instead of the internal pressure sensor 21, 22 within the air space 16, an “external” pressure sensor 27 is used here, which is connected to the air space 16 through a feedthrough 26 via a pressure line 28. Because the air pressure within the air space 16 is approximately equal to an air pressure in a measurement space at the pressure sensor 27 through the pressure line 28, a pressure value representative of the air space 16 can be measured by the pressure sensor 27. Pressure values measured by the pressure sensor 27 are then fed to an evaluation unit 29.

[0063] FIG. 7 shows a modification of the fourth exemplary embodiment of an electric motor 1′″ according to the disclosure as shown in FIG. 6. The pressure sensor system used here—similar to FIG. 4—is formed by a differential pressure sensor 31. The pressure in the air space 16 is supplied to a first connection 23 of the differential pressure sensor 31 via the pressure line 28, while the air pressure of the environment 15 is applied to a second connection 24. The acquisition of the actual pressure difference corresponds to the description shown in FIG. 4.

[0064] FIG. 8 shows a block diagram with basic functions of a circuit for implementing an exemplary embodiment of a method according to the disclosure. An evaluation unit 29 detects measured values from the pressure sensor 21, 22, 27, 31 or several pressure sensors and relates them to an engine rotational speed n. The evaluation unit 29 can thus assume the role of data handling (communication) and evaluations (analysis). A memory 30 is connected to the evaluation unit 29 and can be used to store the actual pressure difference, the rotational speed, the parameter and/or a specific state. When analyzing current sensor data, the evaluation unit 29 can refer to values stored in the memory 30.

[0065] The evaluation unit 29 may be the integrated microprocessor of an EC motor, although the communicative and analytical tasks of the present disclosure can also be performed by external computing units. Examples include: a control device, a PLC (Programmable Logic Controller), a gateway, a cloud computer etc.

[0066] The following table shows measured values for a negative pressure p (in Pascal) and the associated rotational speed n. The first column contains the date of the measurement, the fourth column a parameter k, which

[00001]$k=\frac{p}{n^2}$

[0067] has been calculated by:

TABLE-US-00001 Pressure Rotational speed k Measurement [Pa] [1/min] [10{circumflex over ( )}−4] Jan. 1, 2018 262 2500 0.419 Feb. 1, 2018 252 2500 0.403 Mar. 1, 2018 240 2500 0.384 Apr. 1, 2018 232 2500 0.371 May 1, 2018 132 1950 0.347 Jun. 1, 2018 210 2500 0.336 Jul. 1, 2018 192 2500 0.307 Aug. 1, 2018 95 1950 0.250

[0068] These values of the parameter are plotted in the diagram according to FIG. 9. The parameter k can be understood as a key figure for the cleanliness of the engine. The smaller the value of this parameter k, the lower the cleanliness of the electric motor, or the higher its pollution.

[0069] If the electric motor has been put into operation on Jan. 1, 2018, the parameter k=0.419.Math.10.sup.−4 corresponds to a clean motor, a normal state. Threshold values can be defined above which the normal state no longer exists. Threshold values 0.300 and 0.375 can be defined wherein, for example, at 0.300<k<0.375 the engine is classified as “dirty” and at k<0.300 the engine is classified as “heavily dirty”. This means that the engine will be in “normal state” until Mar. 1, 2018. On Apr. 1, 2018, the first threshold value will fall below 0.375 for the first time, so that a warning message can indicate a slightly dirty engine. On Aug. 1, 2018, the second threshold value falls below 0.300, so a warning message may indicate a heavily dirty engine.

[0070] FIG. 10 shows such a different scenario. Mechanical damage occurred between Apr. 1, 2018 and May 1, 2018, causing the engine to draw false air. As a result, the pressure difference is approximately 0. In this scenario, the state “leaking” can be concluded on May 1, 2018. A warning message can trigger maintenance of the electric motor.

[0071] With regard to further advantageous embodiments of the method according to the disclosure, the electric motor according to the disclosure and the fan according to the disclosure, reference is made to the general part of the description and to the appended claims in order to avoid repetition.

[0072] Finally, it should be expressly noted that the above-described exemplary embodiments serve only to discuss the claimed teaching, but do not limit it to the exemplary embodiments.

LIST OF REFERENCE NUMBERS

[0073] 1, 1′, 1″, 1′″ Electric motor [0074] 2 Stator [0075] 3 Rotor [0076] 4 Stator bushing [0077] 5 Electronics housing [0078] 6 Motor electronics [0079] 7 End cover [0080] 8 Motor axis [0081] 9 Bearing [0082] 10 Bearing [0083] 11 Cooling wheel [0084] 12 Motor housing [0085] 13 Range (air outlet) [0086] 14 Bearing tube [0087] 15 Environment [0088] 16 Air space [0089] 17 Clean motor curve [0090] 18 Dirty motor curve [0091] 19 Curve for heavily dirty motor [0092] 20 Curve with “leaking” motor [0093] 21 Absolute pressure sensor [0094] 22 Differential pressure sensor [0095] 23 First connection [0096] 24 Second connection [0097] 25 Pressure line [0098] 26 Feedthrough [0099] 27 External pressure sensor [0100] 28 Pressure line [0101] 29 Evaluation unit [0102] 30 Memory [0103] 31 External differential pressure sensor