Electric motor

Abstract

The present invention detects a discharge phenomenon of a bearing with high accuracy. This electric motor (10) comprises: a stator (11) having a stator core (11a) on which a winding (11b) is wound; a rotor (12) having a shaft (14) and a rotary body (13) provided to face the stator (11); first and second bearings (15a, 15b) which are a pair of bearings; first and second brackets (19a, 19b) which are a pair of brackets and respectively fix outer rings (17) of the pair of bearings; a conductor (21); and a current detector (22). Each of the pair of bearings has an inner ring (16) and an outer ring (17), and supports the shaft (14) on the inner ring (16). The conductor (21) electrically connects the outer ring (17) of the first bearing (15A) and the outer ring (17) of the second bearing (15B) or the stator core (11a). The current detector (22) detects a discharge current flowing through the conductor (21) accompanying a discharge in the first bearing (15A) or the second bearing (15B).

Description

electric motor

[0001] The present disclosure relates to electric motors.

[0002] Conventionally, there has been known an electric motor including a stator, a rotor having a shaft, a bearing supporting the shaft, and two brackets for fixing the bearing (see, for example, Patent Document 1). In the electric motor of Patent Document 1, the two brackets are conductive and electrically connected to each other. A conductive pin is used for this electrical connection.

[0003] Japanese Patent No. 5338641

[0004] Incidentally, electric motors (particularly electric motors driven by pulse width modulation (PWM) inverters) can experience discharges inside bearings. When discharges occur, the discharge current causes electrolytic corrosion inside the bearing. As the electrolytic corrosion inside the bearing progresses, abnormal noise begins to be generated from the bearing. This series of phenomena is one of the main causes of malfunctions in electric motors. Therefore, it is desirable to accurately detect the discharge phenomenon in the bearing, for example, to monitor the progress of the electrolytic corrosion. In this situation, one of the objects of the present disclosure is to provide an electric motor that can accurately detect the discharge phenomenon in the bearing.

[0005] An electric motor according to one aspect of the present disclosure includes a stator, a rotor, a pair of bearings, a pair of brackets, a conductor, and a current detection unit. The stator has a stator core around which a winding is wound. The rotor is disposed opposite the stator and has a rotating body and a shaft. Each of the pair of bearings has an inner ring and an outer ring, and the inner ring supports the shaft. One of the pair of brackets fixes the outer ring of one of the pair of bearings, and the other fixes the outer ring of the other of the pair of bearings. The conductor electrically connects the outer ring of one of the pair of bearings to the outer ring or the stator core of the other of the pair of bearings. The current detection unit detects a discharge current flowing through the conductor due to discharge in the bearings.

[0006] According to the present disclosure, it is possible to detect the discharge phenomenon in the bearing with high accuracy.

[0007] Fig. 1 is a cross-sectional view schematically showing an electric motor of embodiment 1. Fig. 2 is a block diagram showing the configuration of a control board (control unit) and the like in embodiment 1. Fig. 3 is a cross-sectional view schematically showing an electric motor of embodiment 2. Fig. 4 is a cross-sectional view schematically showing an electric motor of embodiment 3.

[0008] An embodiment of an electric motor according to the present disclosure will be described below using examples. However, the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be used as examples, but other numerical values ​​and materials may be used as long as the effects of the present disclosure are obtained.

[0009] The electric motor according to the present disclosure includes a stator, a rotor, a pair of bearings, a pair of brackets, a conductor, and a current detector.

[0010] The stator has a stator core around which a winding is wound. The stator core may be made of a magnetic material such as a laminated steel plate or a powder magnetic core. The stator core may have a back yoke portion and a plurality of teeth protruding from the back yoke portion. The winding may be wound around the teeth of the stator core. The winding method may be, for example, a concentrated winding method or a distributed winding method.

[0011] The rotor is disposed opposite the stator. The rotor may face the stator in the radial direction of the motor, or may face the stator in the axial direction of the motor. The rotor has a rotating body and a shaft. The rotating body may have a rotating body core made of a magnetic material such as a laminated steel plate or a powder magnetic core. The rotating body may further have at least one permanent magnet fixed to the rotating body core. The rotor may be, for example, a surface magnet type rotor. The shaft may be fixed to the rotating body. The shaft may be made of a magnetic material or a non-magnetic material. The shaft may be conductive.

[0012] Each of the pair of bearings has an inner ring and an outer ring. Each of the pair of bearings supports a shaft with the inner ring. Each of the inner ring and the outer ring may be electrically conductive. The bearing may further have electrically conductive rolling elements (e.g., made of metal) provided between the inner ring and the outer ring. The bearing may be any type of rolling bearing. The bearing may be, for example, a radial ball bearing, but is not limited to this. The pair of bearings may be the same type of bearing or different types of bearing.

[0013] The pair of brackets may be conductive or insulating. The pair of brackets may be made of, for example, metal or insulating resin. The outer rings of a pair of bearings are fixed to the pair of brackets. Specifically, the outer ring of one bearing is fixed to one bracket, and the outer ring of the other bearing is fixed to the other bracket. As a result, if the brackets are conductive, one bracket is electrically connected to the outer ring of one bearing, and the other bracket is electrically connected to the outer ring of the other bearing.

[0014] The conductor electrically connects the outer ring of one bearing to the outer ring or stator core of the other bearing. The conductor may be made of, for example, metal. The conductor may be made of a single component or multiple components. The conductor may have, for example, a lead wire or a conductive tape. When a discharge occurs in the bearing, a pulsed discharge current flows through such a conductor. The discharge current flowing through this conductor is equivalent to the discharge current flowing between the outer ring and inner ring inside the bearing.

[0015] The current detection unit detects the discharge current flowing in the conductor due to discharge in the bearing. In other words, the current detection unit directly detects the discharge current flowing between the outer ring and inner ring inside the bearing. This allows for more accurate detection of the discharge phenomenon in the bearing than when the discharge current is indirectly detected by some means. Based on the highly accurate detection results of the discharge phenomenon, it becomes possible to monitor the progress of electrolytic corrosion inside the bearing. Furthermore, because the current detection unit detects the current flowing in the conductor, which is a fixed member, it does not need to include mechanical elements that come into contact with moving parts such as a shaft. This makes it easy to realize a maintenance-free, highly reliable current detection unit.

[0016] The electric motor may further include a first determination unit that determines the magnitude of the discharge current based on the detection value of the current detection unit. The first determination unit may determine that the greater the absolute value of the detection value, the greater the discharge current. Here, the greater the discharge current, the greater the extent to which electrolytic corrosion progresses inside the bearing due to the discharge. Therefore, by determining the magnitude of the discharge current, the progress of electrolytic corrosion inside the bearing can be monitored in more detail.

[0017] The electric motor may further include a second determination unit that determines the direction of the discharge current based on the detection value of the current detection unit. The second determination unit may determine the direction of the discharge current depending on whether the detection value is positive or negative. Here, the extent to which electrolytic corrosion inside the bearing due to the discharge varies depending on the direction of the discharge current. Therefore, by determining the direction of the discharge current, the progress of electrolytic corrosion inside the bearing can be monitored in more detail.

[0018] The electric motor may further include a counting unit that counts the number of times the discharge current is detected based on the detection value of the current detection unit. The counting unit may increment the number of detections by one each time the absolute value of the detection value exceeds a predetermined threshold. Here, the more discharge current flows, the more electrolytic corrosion progresses inside the bearing. Therefore, by counting the number of times the discharge current is detected, the progress of electrolytic corrosion inside the bearing can be monitored in more detail.

[0019] The electric motor may further include a notification unit that notifies an external device when the number of detections counted by the counting unit exceeds a first threshold. With this configuration, for example, when the degree of progression of electrolytic corrosion is likely to exceed an allowable level (i.e., when maintenance of the electric motor is required), the external device can be notified. The user can receive the notification from the notification unit and perform maintenance of the electric motor at an appropriate time.

[0020] The electric motor may further include a counting unit that counts the number of times the discharge current is detected based on the detection value of the current detection unit, and that, when counting the number of times the discharge current is detected, calculates the product (w·C) of a coefficient w (e.g., a value between 1 and 10) proportional to the magnitude of the discharge current and a predetermined constant C (e.g., 1). This counting method takes into account both the magnitude of the discharge current and the number of times it is detected, making it possible to monitor the progress of electrolytic corrosion inside the bearing in even greater detail.

[0021] The electric motor may further include a notification unit that notifies an external device when the integrated value accumulated by the counting unit exceeds the second threshold. With this configuration, for example, when the degree of progression of electrolytic corrosion is likely to exceed an allowable level (i.e., when maintenance of the electric motor is required), the external device can be notified. The user can receive the notification from the notification unit and perform maintenance of the electric motor at an appropriate time.

[0022] The current detection unit may include a current sensor that detects the current flowing in the conductor. This configuration can prevent erroneous detection of the discharge current due to noise, etc. The current sensor may be a current transformer (CT type) current sensor.

[0023] The current detection unit may include a shunt resistor for detecting the current flowing through the conductor. This configuration can prevent erroneous detection of the discharge current due to noise or the like.

[0024] The stator may be molded with insulating resin. At least a portion of the conductor may be disposed inside the insulating resin. With this configuration, the conductor can be firmly fixed by the insulating resin (molding resin). The insulating resin may include, for example, epoxy resin.

[0025] The stator may be molded with insulating resin, and the conductor and current detector may be disposed outside the insulating resin. With this configuration, the components required for the technology of the present disclosure, i.e., the conductor and current detector, can be easily applied to existing electric motors.

[0026] The pair of brackets may be electrically conductive. One end of the conductor may be connected to one of the brackets. The other end of the conductor may be connected to the other bracket. Alternatively, the other end of the conductor may be connected to the stator core. Alternatively, the other end of the conductor may be connected to the outer ring of a bearing fixed to the other bracket.

[0027] One end of the conductor may be connected to the outer ring of one bearing, and the other end of the conductor may be connected to the outer ring of the other bearing, or the other end of the conductor may be connected to the stator core.

[0028] As described above, according to the present disclosure, by directly detecting the discharge current generated in the bearing, it is possible to detect the discharge phenomenon in the bearing with high accuracy. Furthermore, according to the present disclosure, it is possible to monitor the progress of electrolytic corrosion inside the bearing based on the detection results. Furthermore, according to the present disclosure, it is possible to easily realize a maintenance-free and highly reliable current detection unit.

[0029] An example of an electric motor according to the present disclosure will be described in detail below with reference to the drawings. The components described above can be applied to the components of the example electric motor described below. The components of the example electric motor described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiment. Of the components of the example electric motor described below, components that are not essential to the electric motor according to the present disclosure may be omitted. Note that the drawings shown below are schematic and do not accurately reflect the shapes and number of actual components.

[0030] <<Embodiment 1>> Embodiment 1 of the present disclosure will be described. FIG. 1 is a cross-sectional view that schematically shows an electric motor 10 of embodiment 1. FIG. 2 is a block diagram that shows the configuration of a control board (control unit) and the like in the electric motor 10 of embodiment 1. The electric motor 10 of this embodiment is a radial gap type electric motor, but the technology of this disclosure is also applicable to an axial gap type electric motor. Furthermore, the electric motor 10 of this embodiment is an inner rotor type electric motor, but the technology of this disclosure is also applicable to an outer rotor type electric motor. The electric motor 10 may be, for example, a concentrated winding type three-phase synchronous motor, but is not limited thereto.

[0031] As shown in Figures 1 and 2, the electric motor 10 includes a stator 11, a rotor 12, a first bearing 15A and a second bearing 15B that constitute a pair of bearings, a first bracket 19A and a second bracket 19B that constitute a pair of brackets, a conductor 21, a current detection unit 22, an insulating resin 23, and a control board 24.

[0032] The stator 11 has a stator core 11a around which a winding 11b is wound. The stator core 11a is made of laminated steel plates. The stator core 11a has a generally cylindrical shape. The stator core 11a has a back yoke portion 11a1 and a plurality of teeth 11a2 that protrude radially inward from the back yoke portion 11a1. The winding 11b is wound around the teeth 11a2 of the stator core 11a using a concentrated winding method.

[0033] The rotor 12 is disposed opposite the stator 11. The rotor 12 faces the stator 11 in the radial direction of the electric motor 10. The rotor 12 is disposed inside the stator 11. The rotor 12 has a substantially cylindrical rotor 13 and a shaft 14 fixed thereto. The rotor 13 has a rotor core 13a made of laminated steel plates and a plurality of permanent magnets 13b fixed to the rotor core 13a. The shaft 14 is made of a conductive non-magnetic material.

[0034] Each of first bearing 15A and second bearing 15B has an inner ring 16, an outer ring 17, and a plurality of rolling elements 18 provided between them. Each of first bearing 15A and second bearing 15B rotatably supports shaft 14 with inner ring 16. Inner ring 16, outer ring 17, and rolling elements 18 are each electrically conductive. Both first bearing 15A and second bearing 15B are radial ball bearings.

[0035] The first bracket 19A and the second bracket 19B constituting the pair of brackets are each made of a conductive metal. The outer ring 17 of the first bearing 15A, which is one of the bearings, is fixed to the first bracket 19A, which is one of the brackets. This establishes electrical continuity between the first bracket 19A and the outer ring 17 of the first bearing 15A. The outer ring 17 of the second bearing 15B, which is the other bearing, is fixed to the second bracket 19B, which is the other bracket. This establishes electrical continuity between the second bracket 19B and the outer ring 17 of the second bearing 15B.

[0036] The conductor 21 is made of a metal lead wire. The conductor 21 electrically connects the outer ring 17 of the first bearing 15A and the outer ring 17 of the second bearing 15B. Specifically, one end of the conductor 21 is connected to the first bracket 19A, and the other end of the conductor 21 is connected to the second bracket 19B. This allows the conductor 21 to achieve this electrical connection. A pulsed discharge current flows through the conductor 21 when a discharge occurs in the first bearing 15A or the second bearing 15B. This discharge current is equivalent to the discharge current flowing between the outer ring 17 and the inner ring 16 inside the first bearing 15A and the second bearing 15B.

[0037] The current detection unit 22 detects the discharge current flowing in the conductor 21 due to discharge in the first bearing 15A or the second bearing 15B. In other words, the current detection unit 22 directly detects the discharge current flowing between the outer ring 17 and the inner ring 16 inside the first bearing 15A and the second bearing 15B. The current detection unit 22 has a current sensor 22a that detects the current flowing in the conductor 21. The current sensor 22a is a CT type current sensor and is fixed to the control board 24. The detection value of the current detection unit 22 is input to a computing device (described below) of the control board 24 via an amplifier as necessary.

[0038] The insulating resin 23 molds the stator 11. The insulating resin 23 fixes the second bracket 19B. The first bracket 19A is fixed to the insulating resin 23 by, for example, press-fitting. At least a portion (e.g., the entirety) of the conductor 21 is disposed inside the insulating resin 23.

[0039] The control board 24 has a calculation device and a storage device storing a program executable by the calculation device. The calculation device functions as each functional block by executing the program. As shown in FIG. 2 , each functional block includes a first identification unit 25, a second identification unit 26, a counting unit 27, and a notification unit 28. The control board 24 is an example of a control unit.

[0040] The first specifying unit 25 specifies the magnitude of the discharge current based on the detection value of the current detection unit 22. The first specifying unit 25 determines that the larger the absolute value of the detection value, the larger the discharge current.

[0041] The second specifying unit 26 specifies the direction of the discharge current based on the detection value of the current detection unit 22. The second specifying unit 26 specifies the direction of the discharge current depending on whether the detection value is positive or negative.

[0042] The counting unit 27 counts the number of times the discharge current is detected based on the detection value of the current detecting unit 22. The counting unit 27 increments the number of times the detection is performed by one each time the absolute value of the detection value exceeds a predetermined threshold value.

[0043] When the number of detections counted by the counting unit 27 exceeds the first threshold, the notification unit 28 notifies the outside that the number of detections has exceeded the first threshold. The notification unit 28 may notify the outside that the number of detections has exceeded the first threshold, for example, by outputting a predetermined signal for operating an external device (for example, an output monitor).

[0044] When counting the number of times the discharge current is detected based on the detection value of the current detection unit 22, the count unit 27 may calculate the product w·C of a coefficient w proportional to the magnitude of the discharge current and a predetermined constant C. In this case, the notification unit 28 may notify an external device when the integrated value calculated by the count unit 27 exceeds a second threshold. Here, the second threshold may be the same as or different from the first threshold.

[0045] Second Embodiment A second embodiment of the present disclosure will be described. Fig. 3 is a cross-sectional view that schematically shows an electric motor 10 of the second embodiment. The electric motor 10 of this embodiment differs from the first embodiment in the configuration of the conductor 21. The following mainly describes the differences from the first embodiment.

[0046] 3, one end of the conductor 21 is connected to the first bracket 19A, and the other end of the conductor 21 is connected to the stator core 11a. This allows the conductor 21 to electrically connect between the outer ring 17 of the first bearing 15A and the stator core 11a. In this configuration, a discharge current flows through the conductor 21 in response to a discharge at the first bearing 15A. This discharge current is directly detected by the current detector 22.

[0047] Third Embodiment A third embodiment of the present disclosure will be described. Fig. 4 is a cross-sectional view that schematically shows an electric motor 10 of the third embodiment. The electric motor 10 of the present embodiment differs from the first embodiment in the arrangement of the conductor 21 and the current detection unit 22. The following mainly describes the differences from the first embodiment.

[0048] As shown in Fig. 4, the conductor 21 and the current detection unit 22 are disposed outside the insulating resin 23. One end of the conductor 21 is connected to the first bracket 19A, and the other end of the conductor 21 is connected to the second bracket 19B. This allows the conductor 21 to establish electrical connection between the outer ring 17 of the first bearing 15A and the outer ring 17 of the second bearing 15B. In this configuration, a discharge current flows through the conductor 21 in response to a discharge at the first bearing 15A or the second bearing 15B. This discharge current is directly detected by the current detection unit 22.

[0049] The present disclosure can be used in electric motors.

[0050] DESCRIPTION OF SYMBOLS 10: Electric motor 11: Stator 11a: Stator core 11a1: Back yoke portion 11a2: Teeth portion 11b: Winding 12: Rotor 13: Rotor 13a: Rotor core 13b: Permanent magnet 14: Shaft 15A: First bearing 15B: Second bearing 16: Inner ring 17: Outer ring 18: Rolling element 19A: First bracket 19B: Second bracket 21: Conductor 22: Current detection unit 22a: Current sensor 23: Insulating resin 24: Control board (control unit) 25: First identification unit 26: Second identification unit 27: Counting unit 28: Notification unit

Claims

1. a stator having a stator core wound with a winding; a rotor provided opposite the stator and having a rotating body and a shaft; a pair of bearings each having an inner ring and an outer ring, the inner ring supporting the shaft; a pair of brackets, one of which fixes the outer ring of one of the pair of bearings and the other of which fixes the outer ring of the other of the pair of bearings; a conductor that electrically connects the outer ring of one of the pair of bearings to the outer ring of the other of the pair of bearings or the stator core; a current detection unit that detects a discharge current that flows through the conductor in association with discharge in the bearing.

2. The electric motor according to claim 1 , further comprising a first specifying unit that specifies the magnitude of the discharge current based on a detection value of the current detection unit.

3. The electric motor according to claim 1 , further comprising a second specifying unit that specifies a direction of the discharge current based on a detection value of the current detection unit.

4. 3. The electric motor according to claim 1, further comprising a counting unit that counts the number of times the discharge current is detected based on the detection value of the current detecting unit.

5. The electric motor according to claim 4 , further comprising a notification unit that notifies an external device when the number of detections counted by the counting unit exceeds a first threshold value.

6. 3. The electric motor according to claim 1, further comprising a counting unit that counts the number of times the discharge current is detected based on the detection value of the current detection unit, and that, when counting the number of times the detection is performed, adds up the product of a coefficient proportional to the magnitude of the discharge current and a predetermined constant.

7. The electric motor according to claim 6 , further comprising a notification unit that notifies an external device when the integrated value accumulated by the counting unit exceeds a second threshold value.

8. 3. The electric motor according to claim 1, wherein the current detection unit includes a current sensor that detects a current flowing through the conductor.

9. The stator is molded with insulating resin, The electric motor according to claim 1 or 2, wherein at least a portion of the conductor is disposed inside the insulating resin.

10. The stator is molded with insulating resin, The electric motor according to claim 1 or 2, wherein the conductor and the current detection portion are disposed outside the insulating resin.

11. the pair of brackets are electrically conductive; One end of the conductor is connected to one of the pair of brackets, The electric motor according to claim 1 or 2, wherein the other end of the conductor is connected to the other of the pair of brackets.

12. the pair of brackets are electrically conductive; One end of the conductor is connected to one of the pair of brackets, 3. The electric motor according to claim 1, wherein the other end of the conductor is connected to the stator core.