Bearing condition detection device, rotary electric machine, and bearing condition detection method

Abstract

A bearing condition detection device (200) according to the present disclosure is provided with: a sensor (50) that measures at least one of a magnetic field and an electric field around a bearing (20) which has a cylindrical shape and supports a shaft (12) of a rotor (10) of a rotary electric machine (100) on the inner circumferential surface; and a shaft current detection unit (70) that detects, on the basis of a signal from the sensor (50), a shaft current which flows through the bearing (20). The sensor (50) is disposed so as to face at least one end surface (20fe) of both end surfaces in the axial direction of the bearing (20).

Description

Bearing condition detection device, rotating electrical machine, and bearing condition detection method

[0001] The present disclosure relates to a bearing condition detection device, a rotating electrical machine, and a bearing condition detection method.

[0002] In rotating electrical machines driven by a power conversion circuit using an inverter, the switching operation of semiconductor elements included in the inverter causes electrolytic corrosion of the bearings, which causes wear and damage to the bearings and reduces the reliability of the rotating electrical machine.

[0003] It is known that electrolytic corrosion in bearings is caused by axial current, which is a discharge current that flows between the rigid spheres that make up the bearing and the inner and outer rings. However, because axial current propagates from the bearing to the housing that holds the bearing, direct measurement is difficult. In response to this, a technique has been disclosed for indirectly measuring axial current by placing a magnetic field sensor close to a magnetized bearing and detecting changes in the magnetic field caused by axial current (see, for example, Patent Document 1). Another technique has also been disclosed for highly sensitively detecting axial current by combining a magnetic field sensor and an acoustic sensor (see, for example, Patent Document 2).

[0004] JP 2011-39056 A (paragraphs 0016 to 0024, Figures 1 to 5) WO 2016 / 157347 (paragraphs 0024 to 0027, Figure 1)

[0005] However, magnetizing the bearing requires additional equipment, which increases the number of parts and costs, and there is also the issue that simply placing a magnetic field sensor close to the bearing reduces the detection sensitivity for the axial current propagating from the bearing to the housing.Furthermore, combining an acoustic sensor also requires additional equipment such as an acoustic sensor, which increases the number of parts and costs.

[0006] The present disclosure discloses a technique for solving the above-described problems, and aims to detect axial current with high sensitivity without increasing the number of parts.

[0007] The bearing condition detection device disclosed herein comprises a cylindrical sensor that measures at least one of the magnetic field and the electric field around a bearing that supports the rotor shaft of a rotating electric machine on its inner surface, and an axial current detection unit that detects the axial current flowing through the bearing based on a signal from the sensor, wherein the sensor is arranged opposite at least one of both end faces in the axial direction of the bearing.

[0008] The bearing condition detection method disclosed herein is characterized by including a step of placing a sensor that measures at least one of a magnetic field and an electric field, facing at least one of both axial end faces of a bearing that supports the rotor shaft of a rotating electric machine, and a step of detecting an axial current flowing radially through the bearing based on a signal from the sensor.

[0009] According to the bearing condition detection device or bearing condition detection method of the present disclosure, the sensor is arranged to face the axial end face of the bearing, so that axial current can be detected with high sensitivity without increasing the number of parts.

[0010] 2A and 2B are a block diagram illustrating a bearing condition detection device according to a first embodiment and a rotating electric machine equipped with the bearing condition detection device, together with a cross-sectional view including the shaft of the rotating electric machine. FIGS. 2A and 2B are a top view and a cross-sectional view including the shaft, respectively, of a bearing that is a detection target of the bearing condition detection device or bearing condition detection method according to the first embodiment. FIGS. 2A and 2B are a cross-sectional view perpendicular to the shaft of a rotating electric machine that is a target of the bearing condition detection device according to the first embodiment. FIGS. 2B and 2C are a block diagram illustrating a rotating electric machine that is a target of the bearing condition detection device according to the first embodiment and a drive circuit thereof. FIGS. 2C and 2D are an equivalent circuit diagram illustrating the principle of shaft voltage generation in a rotating electric machine. FIGS. 2D and 2E are a cross-sectional view including the shaft showing an example of a shaft current path in a rotating electric machine. FIGS. 2D and 2E are a cross-sectional view including the shaft showing an example of a shaft current path when a load is connected to the rotating electric machine. FIGS. 2D and 2E are a top view and a cross-sectional view including the shaft, respectively, of a bearing that is a detection target of the bearing condition detection device according to the first embodiment, when a conductive seal plate is provided on the bearing. FIGS. 2D and 2C are a cross-sectional view including the shaft showing another example of a sensor placement in the bearing condition detection device according to the first embodiment. Fig. 1 is a block diagram showing the hardware configuration of a bearing condition detection device according to a first embodiment. Fig. 2 is a block diagram showing a bearing condition detection device according to a second embodiment and a rotating electric machine equipped with the bearing condition detection device, together with a cross-sectional view including the shaft of the rotating electric machine. Fig. 3 is a block diagram showing a bearing condition detection device according to a third embodiment and a rotating electric machine equipped with the bearing condition detection device, together with a cross-sectional view including the shaft of the rotating electric machine.

[0011] 1 to 9 are diagrams for explaining the configuration of a bearing condition detection device and a rotating electric machine equipped with the bearing condition detection device, and a bearing condition detection method according to a first embodiment, with Fig. 1 being a block diagram showing the bearing condition detection device and the rotating electric machine equipped with the bearing condition detection device, along with a cross-sectional view including the shaft of the rotating electric machine, Fig. 2A being a top view when the axial direction of the bearing to be detected is the up-down direction, and Fig. 2B being a cross-sectional view taken along line B-B of Fig. 2A, including the shaft.

[0012] 3 is a cross-sectional view taken along line A-A in FIG. 1, which is perpendicular to the axis of the rotating electric machine on which the bearing condition detection device is to be installed; FIG. 4 is a block diagram showing the rotating electric machine on which the bearing condition detection device is to be installed and its drive circuit; and FIG. 5 is an equivalent circuit diagram showing the principle of shaft voltage generation in the rotating electric machine.

[0013] FIG. 6 is a cross-sectional view corresponding to FIG. 1 , including an axis, showing an example of an axial current path in a rotating electric machine. FIG. 7 is a cross-sectional view including an axis, showing an example of an axial current path when a load is connected to a motor, which is a rotating electric machine. FIG. 8 is a partially enlarged cross-sectional view of a portion of FIGS. 6 and 7 , including an axis, showing an example of sensor placement relative to a bearing in a bearing condition detection device. FIG. 9A is a top view showing a preferred embodiment when a conductive seal plate is provided on a bearing. FIG. 9B is a schematic cross-sectional view including an axis corresponding to line CC in FIG. 9A. FIGS. 9A and 9B are schematic cross-sectional views corresponding to FIG. 2B, each showing two preferred embodiments of a conductive seal plate when a bearing is provided with a conductive seal plate. FIG. 10 is a partially enlarged cross-sectional view corresponding to FIG. 8 , including an axis, showing another example of sensor placement.

[0014] 1, a bearing condition detection device 200 according to a first embodiment detects an axial current flowing through a bearing 20A that rotatably supports a rotor 10 of a rotating electrical machine 100. Before describing the bearing condition detection device 200 in detail, the structure of the bearing 20 (when there is no need to distinguish between the two bearings 20A and 20B, they will be referred to as bearing 20) that is the detection target will be described.

[0015] 2A and 2B , bearing 20 has an inner ring 21, a plurality of rigid balls 22 serving as rolling elements, and an outer ring 23, with the plurality of rigid balls 22 loaded between the inner ring 21 and the outer ring 23. Bearing 20 is cylindrical and has an outer peripheral surface 20fo, an inner peripheral surface 20fi, and a pair of end faces 20fe at both ends in the axial direction (direction along axis Xr), with inner peripheral surface 20fi tightly fixed to shaft 12 of rotating electric machine 100, and the plurality of rigid balls 22 rolling about axis Xr. Furthermore, the plurality of rigid balls 22 roll together with lubricating oil (not shown) filled between inner ring 21 and outer ring 23, allowing rolling with little friction.

[0016] At this time, an oil film of lubricating oil, which is an insulator, is formed between the inner ring 21 and the rigid balls 22, and between the rigid balls 22 and the outer ring 23. In this embodiment, a rolling bearing is used in which the rigid balls 22 are balls, but this is not limited to this and other rolling elements such as cylindrical rollers or needle rollers may be used. Also, a bearing other than a rolling bearing, such as a sliding bearing, may be used.

[0017] Based on the configuration of bearing 20 described above, the configuration of rotating electric machine 100, which is a rotating electric machine, and bearing condition detection device 200 will be described with reference to Fig. 1 and Fig. 3. Rotating electric machine 100 depicted in Fig. 1 and Fig. 3 has the configuration of a so-called brushless motor. Rotating electric machine 100 has a housing 40, a stator 30, a rotor 10 arranged radially inward of stator 30, and bearings 20A and 20B fixed to housing 40 and supporting rotor 10 for free rotation.

[0018] Of the end faces 20fe of each bearing 20, the one facing the inside of the housing 40 is referred to as the inner end face 20fei, and the one facing the outside is referred to as the outer end face 20fex. The bearing condition detection device 200 has a sensor 50 that faces the end face 20fe of the bearing 20, and an axial current detection unit 70 that receives a signal from the sensor 50 via a transmission unit 200w and detects the presence or absence of an axial current, but before going into details, the rotating electric machine 100 will be described.

[0019] The stator 30 is composed of a stator core 31 and a stator winding 32. The stator core 31 includes an annular core back portion 31b, teeth 31t extending radially inward from the inner circumferential surface of the core back portion 31b, and flanges 31g protruding circumferentially from the tips of the teeth 31t. The radial direction refers to a direction that is perpendicular to the axis Xr and extends radially from the axis Xr as the origin, and the circumferential direction refers to a direction along the circumference of a concentric circle that also has the axis Xr as the origin.

[0020] The stator core 31 is obtained, for example, by stacking thin electromagnetic steel sheets in the axial direction and integrating them. The stator winding 32 is wound around the teeth 31t and housed in slots 31s formed between adjacent teeth 31t. The portions of the stator winding 32 that protrude axially from the outermost layer of the stator core 31 are called coil ends. The winding method for the stator winding 32 includes a winding method called concentrated winding, in which the stator winding 32 is wound around each tooth 31t, and a winding method called distributed winding, in which the stator winding 32 is wound across multiple teeth 31t. Regardless of the winding method, the effect of detecting axial current with high sensitivity, described below, can be obtained in the same way.

[0021] The enclosure 40 is composed of a housing 41 and brackets 42A and 42B. The housing 41 has a cylindrical shape, and the inner peripheral surface of the housing 41 and the outer peripheral surface of the core back portion 31b of the stator core 31 are fixed together so that they face each other. The housing 41 and the core back portion 31b of the stator core 31 are electrically connected.

[0022] Brackets 42A, 42B are fastened with bolts or the like to both ends of housing 41, i.e., to the openings on the load connection side and the non-load connection side. Brackets 42A, 42B are fixed to the outer peripheral surfaces of the outer rings 23 of bearings 20A, 20B, respectively. The integrated housing 41 and brackets 42A, 42B form the housing 40 of the rotating electric machine 100, and house the rotor 10, bearings 20, and stator 30 therein.

[0023] The rotor 10 includes a rotor core 11, a plurality of permanent magnets 13 embedded near the outer periphery of the rotor core 11, and a shaft 12 fixed to a hole that passes through the radial center of the rotor core 11. The rotor core 11 is obtained, for example, by integrally forming thin electromagnetic steel sheets by stacking them in the axial direction. The shaft 12 is fixed to inner rings 21 (inner peripheral surfaces 20fi) of bearings 20A and 20B on both its load-connected side (left side in FIG. 1 ) and its non-load-connected side (right side in FIG. 2 ), and the outer peripheral surfaces 20fo of the bearings 20A and 20B are fixed to the housing 40, thereby being rotatably supported relative to the housing 40.

[0024] Next, the configuration of a drive circuit 500 that drives the rotating electric machine 100 will be described with reference to Fig. 4. The drive circuit 500 is composed of a power supply unit 501, a power conversion circuit 502, wiring 503 connecting them, and wiring 504 connecting the power conversion circuit 502 and the rotating electric machine 100. The power supply unit 501 is a DC power supply that supplies the power necessary to drive the rotating electric machine 100, which is a brushless motor. As the DC power supply, for example, a secondary battery such as a lithium ion battery, a nickel-metal hydride battery, or a lead-acid battery can be used.

[0025] The power conversion circuit 502 is configured with semiconductor switching elements and circuits that drive them. Examples of the switching elements that can be used include insulated gate bipolar transistors (IGBTs) and metal oxide semiconductor field effect transistors (MOSFETs). A converter circuit is configured within the power conversion circuit 502, and adjusts the DC voltage supplied from the power supply unit 501 via wiring 503 to a desired voltage by stepping it up or down to DC power.

[0026] The DC power adjusted to the desired voltage is used to generate a three-phase AC current required to drive the rotating electric machine 100 by adjusting the ratio between the on and off times of semiconductor switching elements used in an inverter circuit configured separately from the converter circuit. This three-phase AC current is supplied to the rotating electric machine 100 via wiring 504. That is, the power conversion circuit 502 functions as a so-called converter circuit and / or inverter circuit. In addition, in order to prevent high-frequency noise generated by the switching operation of the semiconductor switching elements from leaking to the power supply unit 501, the power conversion circuit 502 is provided with a noise filter configured of an inductor and a capacitor as needed.

[0027] Although the present embodiment shows a configuration in which a DC power supply is used for the power supply unit 501, the power supply unit 501 does not need to be a DC power supply and may be an AC power supply. In this case, the power conversion circuit 502 may be provided with a rectifier circuit that receives an AC voltage as input and converts it into a DC voltage of a different voltage, instead of a converter circuit.

[0028] Here, the principle by which shaft voltage V2 is generated in rotating electric machine 100 driven by power conversion circuit 502 will be described using the equivalent circuit of FIG. 5 . Note that shaft voltage V2 here is defined as the voltage of shaft 12 measured with reference to the potential of housing 40. In FIG. 5 , point G represents the potential of housing 40, point N represents the potential of neutral point N of stator winding 32, and point S represents the potential of shaft 12. Voltage V1, which is the potential difference between point N and point G, represents the voltage of neutral point N of rotating electric machine 100, and the potential difference between point S and point G represents shaft voltage V2 of rotating electric machine 100. Furthermore, C1 represents the stray capacitance between stator winding 32 and rotor 10, and C2 represents the stray capacitance between rotor 10 and housing 40.

[0029] To drive the rotating electric machine 100, a group of semiconductor switching elements included in the power conversion circuit 502 performs switching operation at a carrier frequency fc based on PWM (Pulse Width Modulation) control. At this time, the magnitude of the voltage V1 at the neutral point N also fluctuates stepwise over time with a period of the carrier frequency fc. The fluctuation in the voltage V1 at the neutral point N generated between the housing 40 and the stator winding 32 is divided by the stray capacitance C1 and the stray capacitance distributed inside the rotating electric machine 100, and a finite potential difference, i.e., a shaft voltage V2, is induced in the shaft 12 relative to the housing 40.

[0030] The impedance Z of the stray capacitance C at a frequency f can be expressed by equation (1). Z(C) = 1 / (2πfC) (1) Therefore, the axial voltage V2 generated between the housing 40 and the shaft 12 can be expressed by equation (2). V2 = {Z(C2) / (Z(C1) + Z(C2))} x V1 = {C1 / (C1 + C2)} x V1 (2)

[0031] Next, the principle of how axial current is generated in the rotating electric machine 100 driven by the power conversion circuit 502 and an example of its propagation path will be described with reference to Fig. 6. If axial voltage V2 exceeds the breakdown voltage of the bearing 20, or if breakdown occurs due to low-speed rotation of the bearing 20 or the inclusion of foreign matter causing the rigid balls 22 to come into contact with the outer ring 23 and inner ring 21, the electric charge stored in the stray capacitance of the rotating electric machine 100 and bearing 20 will be discharged, causing axial current I1 to flow.

[0032] Axial current I1 is generated due to fluctuations in neutral point voltage V1, and propagates from stator winding 32 through rotor 10, bearings 20A and 20B, and housing 40, before flowing outside rotating electric machine 100, where the potential is the same as the housing potential (point G). Because rotating electric machine 100 has an infinite number of stray capacitances, there are multiple axial current paths other than the one shown by axial current I1, but because the generation of axial current is accompanied by insulation breakdown of bearing 20, whatever the path, the axial current includes at least one of the multiple bearings 20 in its propagation path.

[0033] While this embodiment has shown one example of a propagation path of the axial current I1 that occurs due to fluctuations in the voltage V1 at the neutral point N, this is not intended to be limiting. For example, the bearing condition detection device 200 is also effective for axial currents that occur due to other phenomena, such as axial currents caused by insulation breakdown of the bearing 20 due to frictional charging, and axial currents caused by axial voltage V2 that results from asymmetry in magnetic flux distribution. Furthermore, this embodiment has shown one example of a propagation path in which the axial current I1 flows to the outside of the rotating electric machine 100, which has the same potential as the housing potential, but this is not intended to be limiting. For example, the bearing condition detection device 200 is also effective in cases where the propagation path circulates inside the rotating electric machine 100, as shown in FIG. 10 , which will be described later.

[0034] 7 will be used to describe another example of a propagation path of axial current I1 in rotating electric machine 100 driven by power conversion circuit 502. Load device 900 is driven as a load of rotating electric machine 100 described in FIG. 1 and is connected via load device connection unit 400. Load device 900 includes a shaft 912, a bearing 920, and a housing 940 as some of its components.

[0035] The enclosure 940 includes a housing 941 and a bracket 942A as some of its components. The outer peripheral surface of the bearing 920 is fixed to the bracket 942A, and the inner peripheral surface is fixed to the shaft 912. The shaft 12 of the rotating electric machine 100 and the shaft 912 of the load device 900 are electrically and mechanically connected via the load device connection unit 400. In this configuration, the axial current generated due to fluctuations in the voltage V1 of the neutral point N described in FIG. 6 is divided into an axial current I1 propagating through the bearing 20 of the rotating electric machine 100 and an axial current I2 propagating through the bearing 920 of the load device 900.

[0036] Next, the configurations of the sensor 50 and the axial current detection unit 70 will be described with reference to FIG. 7. The sensor 50 is disposed in a position facing the outer end surface 20fex of the bearing 20A, and is a magnetic field sensor that measures changes in the magnetic field generated due to the axial current I1 flowing through the bearing 20A. The axial current detection unit 70 is connected via a transmission unit 200w that transmits a signal measured by the sensor 50 to the axial current detection unit 70. Note that, although the transmission unit 200w is depicted in a wired form such as an electric cable or optical fiber in this embodiment, it is not limited to this and may include wireless signal transmission means.

[0037] The axial current detection unit 70 detects the axial current (bearing condition) from the signal measured by the sensor 50. Examples of the bearing condition include functions such as detecting the timing of axial current occurrence, calculating the axial current value, monitoring the bearing condition based on the number and frequency of axial current occurrences, and current value information, or diagnosing abnormalities. Although the present embodiment shows an example of the function of the axial current detection unit 70, the technical scope of the present disclosure is not limited by the function of the axial current detection unit 70.

[0038] Next, the arrangement of the sensor 50 will be described with reference to FIG. 8. The sensor 50 detects the magnetic flux φ1 generated due to the axial current I1 propagating radially through the bearing 20A. The sensor 50 is arranged in a position facing the outer end surface 20fex of the bearing 20A, enabling efficient detection of the magnetic flux φ1. Furthermore, from the viewpoint of improving the detection sensitivity of the magnetic flux φ1, it is desirable that the sensor 50 be arranged close to the outer end surface 20fex of the bearing 20A so as to have maximum sensitivity to the magnetic field caused by the current flowing radially through the bearing 20A.

[0039] Here, the end face 20fe may be covered with a conductive sealing plate such as a metal plate or a non-conductive sealing plate such as a rubber seal to protect and seal the rigid spheres 22 and lubricant of the bearing 20. From the viewpoint of improving the detection sensitivity of the magnetic flux φ1, it is desirable that no conductor be interposed between the sensor 50 of the bearing 20 and the opposing end face 20fe.

[0040] Furthermore, when a metal plate sealing plate 25 is provided on the end face 20fe, as shown in Figures 9A and 9B, the sealing plate 25 is configured to be non-contact with at least one of the inner ring 21 and outer ring 23 of the bearing 20, i.e., to prevent a short circuit between the inner ring 21 and the outer ring 23. While the figures show an example in which a gap Sp is provided between the inner ring 21 and the sealing plate 25, an insulating material may be interposed between the inner ring 21 and the sealing plate 25. Furthermore, to avoid a conductor being interposed between the sensor 50 and the end face 20fe, an opening 25a may be provided so that the detection area 50d of the sensor 50 is open to the end face 20fe. Note that if the sealing plate 25 is non-conductive, the same effect as when the opening 25a is provided is achieved.

[0041] As described above, there are multiple propagation paths of the axial current, and each path includes at least one of the multiple bearings 20A, 20B. Because the sensor 50 is disposed in a position facing the end face 20fe of the bearing 20, it is possible to efficiently detect any of the multiple propagation paths of the axial current.

[0042] In this embodiment, the sensor 50 is a magnetic field sensor, but this is not a limitation and the sensor 50 may be an electric field sensor that measures changes in the electric field caused by the axial current. The sensor 50 only needs to measure at least one of the magnetic field and the electric field caused by the axial current. In addition, in this embodiment, the sensor 50 is disposed in a position facing the outer end surface 20fex of the bearing 20, but this is not a limitation and the sensor 50 may be disposed facing the inner end surface 20fei, or may be disposed facing both the outer end surface 20fex and the inner end surface 20fei. Furthermore, in this embodiment, the sensor 50 is disposed relative to the bearing 20A on the load-connected side, but this is not a limitation and the sensor 50 may be disposed relative to the bearing 20B on the non-load-connected side, or may be disposed relative to multiple bearings 20.

[0043] Furthermore, the sensor 50 may include not only a sensor element that detects magnetic flux in a certain direction, but also another sensor element that detects magnetic flux in a direction inclined, for example, at 45° relative to the certain direction. In particular, when another sensor that detects magnetic flux perpendicular to the certain direction is included, the sensor elements may be arranged so that the surface on which the detection area of ​​one sensor element is provided faces the end face 20fe of the bearing 20, and the surface on which the detection area of ​​the other sensor element is provided faces the outer peripheral surface of the shaft 12, as shown in Figures 7 and 8. With this configuration, the sensor 50 can detect not only the magnetic flux φ1 generated by the axial current propagating radially through the bearing 20, but also the magnetic flux φ2 generated by the axial current propagating axially through the shaft 12, thereby further improving detection sensitivity.

[0044] In this case, from the viewpoint of improving the detection sensitivity of the magnetic flux φ2, it is desirable that the sensor 50 be disposed close to the outer peripheral surface of the shaft 12 and be disposed so that the other sensor elements have maximum sensitivity to the magnetic field caused by the current flowing axially through the shaft 12. In other words, by disposing the sensor 50 so that it has maximum sensitivity to both the magnetic field caused by the current flowing radially through the bearing 20 and the magnetic field caused by the current flowing axially through the shaft 12, it is possible to further improve the detection sensitivity.

[0045] In this embodiment, the sensor 50 is arranged for the axial current I2 that propagates to the housing 940 of the load device 900 among the axial currents that flow through the shaft 12 as an example of the axial current that generates the magnetic flux φ2, but this is not limited to this. For example, the sensor 50 may be arranged for the axial current I1 that propagates to the housing 40 of the rotating electric machine 100 as shown in FIG.

[0046] As described above, the sensor 50 has the function of detecting the bearing condition by measuring the shaft current, but may also have the function of detecting other signals. Examples include magnetic rotation angle sensors such as resolvers and encoders. Rotation angle sensors are generally placed in proximity to the bearing 20 on the side not connected to the load. By providing the sensor 50 with the function of detecting the rotation angle of the rotating electric machine 100 in this way, it is possible to reduce the number of sensor components.

[0047] In other words, by placing the sensor 50 in a position opposite the end face 20fe of the bearing 20, where the axial current is generated, the detection sensitivity of the axial current is improved without increasing the number of parts, and the bearing condition can be detected with higher accuracy.

[0048] It is possible that a section that performs calculations, such as the axial current detection unit 70, is configured by a single piece of hardware 700 including a processor 701 and a storage device 702, as shown in FIG. 11 . Although not shown, the storage device 702 includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. Alternatively, a hard disk auxiliary storage device may be used instead of the flash memory. The processor 701 executes a program input from the storage device 702. In this case, the program is input from the auxiliary storage device to the processor 701 via the volatile storage device. The processor 701 may output data such as calculation results to the volatile storage device of the storage device 702, or may store the data in the auxiliary storage device via the volatile storage device.

[0049] Second Embodiment In the first embodiment described above, an example in which one rotating electric machine is equipped with one bearing condition detection device has been described. In the second embodiment, an example in which two bearing condition detection devices are equipped with one rotating electric machine will be described. Figure 12 is a block diagram corresponding to Figure 1 for explaining the configuration of a bearing condition detection device according to the second embodiment. Note that in the second embodiment, the configuration and operation of the rotating electric machine including the bearings, the drive circuit, etc. are the same as in the first embodiment, and therefore a description of similar parts will be omitted, and Figures 2A to 5 of the first embodiment will be used.

[0050] 12, bearing condition detection device 200T according to the second embodiment includes, in addition to first bearing condition detection device 200A which detects the axial current of bearing 20A, second bearing condition detection device 200B which detects the axial current of bearing 20B, and propagation path determination section 60. Both first bearing condition detection device 200A and second bearing condition detection device 200B have the same configuration as that described as bearing condition detection device 200 according to the first embodiment, but the components constituting first bearing condition detection device 200A are distinguished by adding "A" to the end of their reference numerals, and the components constituting second bearing condition detection device 200B are distinguished by adding "B" to the end of their reference numerals.

[0051] The second bearing condition detection device 200B has a sensor 50B disposed opposite the outer end surface 20fex of the bearing 20B and an axial current detection unit 70B that detects the axial current based on the signal output from the sensor 50B. Even with this structure, it is possible to obtain the same effects as the bearing condition detection device 200 shown in Embodiment 1. The sensor 50B is disposed at a position opposite the outer end surface 20fex of the bearing 20B, and is a magnetic field sensor that measures the magnetic field generated due to the axial current flowing through the bearing 20B.

[0052] The bearing condition detection device 200T is also provided with a propagation path determination unit 60 that determines the propagation path of the axial current based on the output from the axial current detection unit 70A and the output from the axial current detection unit 70B. In other words, the first bearing condition detection device 200A, the second bearing condition detection device 200B, and the propagation path determination unit 60 form a single bearing condition detection device 200T. Note that in the second embodiment, the axial current detection unit 70A and the axial current detection unit 70 are expressed as separate units, but this is not limited to this, and at least some of the functions of a plurality of parts that perform arithmetic processing, including the propagation path determination unit, may be integrated.

[0053] Here, the axial current I1 described in Fig. 6 and the axial current I3 shown in Fig. 12 have different current propagation paths. The axial currents flowing in the load-connected bearing 20A and the non-load-connected bearing 20B shown in Fig. 6 both flow from the inner ring 21 to the outer ring 23. In other words, insulation breakdown occurs simultaneously in the load-connected bearing 20A and the non-load-connected bearing 20B. At this time, the detection signals from the sensor 50A provided on the bearing 20A side and the sensor 50B provided on the bearing 20B side have the same sign.

[0054] In contrast, the axial currents flowing in the load-connected side bearing 20A and the unloaded side bearing 20B shown in Fig. 12 flow in opposite directions. Such a propagation path of the axial current occurs when insulation breakdown occurs in either the load-connected side bearing 20A or the unloaded side bearing 20B due to the influence of a foreign object, for example.

[0055] As an example, if dielectric breakdown occurs in bearing 20A on the load-connected side, axial current I3 propagates through a path connecting shaft 12, bearing 20A on the load-connected side, housing 40, and bearing 20B on the non-load-connected side. In this case, the signs of the detection signals from sensor 50B provided on bearing 20A and sensor 50B provided on bearing 20B will be opposite. In this way, since rotating electric machine 100 is provided with sensors 50A and 50B on the multiple bearings 20A and 20B that support shaft 12, respectively, propagation path determiner 60 can determine the propagation path of the axial current from the processing results of the detection signals from each of the multiple sensors 50.

[0056] Furthermore, bearing condition detection device 200T of embodiment 2 is provided with sensors 50A and 50B for a plurality of bearings 20A and 20B, respectively, and is therefore able to monitor the conditions and diagnose abnormalities of a plurality of bearings 20. Furthermore, like bearing condition detection device 200 of embodiment 1, bearing condition detection device 200T of embodiment 2 improves the detection sensitivity of shaft current without increasing the number of parts, and is able to detect the bearing condition with higher accuracy.

[0057] Third Embodiment In the first and second embodiments described above, examples have been described in which the bearing condition is detected based on a signal from a sensor that detects a magnetic field or electric field associated with an axial current. In a third embodiment, an example will be described in which a axial voltage signal is also added to detect the bearing condition. Figure 13 is a block diagram corresponding to Figure 1 for explaining the configuration of a bearing condition detection device according to the third embodiment. Note that in the third embodiment, the configuration and operation of the rotating electric machine including the bearing, the drive circuit, etc. are the same as in the first embodiment, and therefore explanations of similar parts will be omitted, and Figures 2A to 5 of the first embodiment will be used.

[0058] As shown in FIG. 13 , a bearing condition detection device 200 according to the third embodiment differs from the bearing condition detection device 200 of FIG. 1 in that it includes a voltage sensor 80 that measures shaft voltage V2, and a shaft current detection unit 70 that detects the shaft current based on signals from sensor 50 and voltage sensor 80.

[0059] Voltage sensor 80 measures the voltage between shaft 12 and housing 40, i.e., shaft voltage V2 of rotating electric machine 100. Even with this structure, it is possible to obtain the same effects as bearing condition detection device 200 shown in embodiments 1 and 2. The connection point of voltage sensor 80 to shaft 12 uses a member such as a brush or conductive microfiber, which is used to transmit a detection signal from a rotating body such as shaft 12.

[0060] In this way, a signal measured by voltage sensor 80, which detects the voltage between inner ring 21 and outer ring 23 of bearing 20, is transmitted to axial current detection unit 70. This makes it possible to measure not only axial current but also axial voltage V2, and by measuring both axial current and axial voltage V2, a correlation can be derived, and the derived correlation can be used to more accurately monitor the conditions of multiple bearings and diagnose abnormalities. Data on the derived correlation may be stored in a database (not shown) provided in axial current detection unit 70. Furthermore, like bearing condition detection devices 200 of embodiments 1 and 2, bearing condition detection device 200 of embodiment 3 improves axial current detection sensitivity without increasing the number of parts, and can detect bearing conditions with higher accuracy.

[0061] Although various exemplary embodiments and examples are described in this disclosure, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless modifications not illustrated are contemplated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is modified, added, or omitted, or where at least one component is extracted and combined with components of another embodiment.

[0062] As described above, the bearing condition detection device 200 of the present disclosure includes the sensor 50, which is cylindrical and measures at least one of the magnetic field and the electric field around the bearing 20, the inner circumferential surface 20fi of which supports the shaft 12 of the rotor 10 of the rotating electric machine 100, and the axial current detection unit 70, which detects the axial current flowing through the bearing 20 based on a signal from the sensor 50, and the sensor 50 is arranged to face at least one of the end faces 20fe of the bearing 20 in the axial direction. This makes it possible to detect the axial current in the rotating electric machine 100 with high sensitivity without increasing the number of parts.

[0063] The sensor 50 can detect the axial current more reliably if the sensor element is positioned so that it has maximum sensitivity to at least one of the magnetic field and the electric field caused by the current flowing radially through the bearing 20.

[0064] If the sensor 50 is also arranged to face the outer circumferential surface of the shaft 12, it can also detect the current flowing in the axial direction of the shaft 12.

[0065] In this case, if the sensor 50 is arranged so that the second sensor element has maximum sensitivity to at least one of the magnetic fields and electric fields caused by current flowing axially through the shaft 12 (the detection target is perpendicular to the above-mentioned sensor element which has maximum sensitivity to at least one of the magnetic fields and electric fields caused by current flowing radially), the current flowing axially through the shaft 12 can be detected more reliably.

[0066] Furthermore, if the sensor 50 has a function of detecting the rotation angle of the rotor 10, the number of parts can be reduced.

[0067] Sensors 50A and 50B are provided corresponding to the two bearings 20A and 20B that support the shaft 12, respectively, and a propagation path determination unit 60 is provided that determines the propagation path of the axial current depending on the direction of the axial current in each of the two bearings 20 detected by the axial current detection unit 70A and the axial current detection unit 70B, making it easier to monitor the condition of the bearings 20 and diagnose any abnormalities.

[0068] If a voltage sensor 80 is provided that measures the voltage (shaft voltage V2) between the shaft 12 and the housing 40 of the rotating electrical machine 100 that holds the bearing 20, and the axial current detection unit 70 detects the axial current flowing through the bearing 20 based on the signal from the sensor 50 and the signal from the voltage sensor 80, then the correlation between the axial current and the axial voltage V2 can be determined, enabling more accurate monitoring of the condition of the bearing 20 and diagnosis of abnormalities. In this case, it is desirable to detect the axial current using the correlation described above.

[0069] Furthermore, the rotating electric machine 100 of the present disclosure comprises a rotor 10, a stator 30 arranged concentrically with a gap between it and the outer peripheral surface of the rotor 10, and a housing 40 that holds the bearing 20 and the stator 30 from the radial outside and houses the stator 30 and the rotor 10 inside, and by equipping it with the above-mentioned bearing condition detection device 200, the condition of the bearing 20 can be easily diagnosed, increasing reliability.

[0070] In addition, the end face 20fe of the bearing 20 facing the sensor 50 is covered with a conductive sealing plate 25 to protect the lubricant filled between the inner ring 21 and the outer ring 23, and if the sealing plate 25 is insulated from one of the inner ring 21 and the outer ring 23 and the area facing the detection surface of the sensor 50 is open, the magnetic flux detection sensitivity is improved.

[0071] As described above, the bearing condition detection method disclosed herein includes the steps of: disposing sensor 50, which measures at least one of a magnetic field and an electric field, facing at least one of end faces 20fe in the axial direction of bearing 20, which supports shaft 12 of rotor 10 of rotating electric machine 100; and detecting an axial current flowing radially through bearing 20 based on a signal from sensor 50. This makes it possible to detect the axial current in rotating electric machine 100 with high sensitivity without increasing the number of parts.

[0072] 10: Rotor, 100: Rotating electric machine, 12: Shaft, 20: Bearing, 200, 200T: Bearing condition detection device, 20fe: End face, 25: Seal plate, 30: Stator, 40: Housing, 50: Sensor, 60: Propagation path determination unit, 70: Shaft current detection unit, 80: Voltage sensor, 500: Drive circuit, 501: Power supply unit, 502: Power conversion circuit, 900: Load device, 912: Shaft, I1, I2, I3: Shaft current, V2: Shaft voltage, Xr: Shaft, φ1, φ2: Magnetic flux.

Claims

a cylindrical sensor for measuring at least one of a magnetic field and an electric field around a bearing that supports a rotor shaft of a rotating electric machine on its inner circumferential surface; an axial current detection unit that detects an axial current flowing through the bearing based on a signal from the sensor, The bearing condition detection device is characterized in that the sensor is disposed opposite at least one of both end faces of the bearing in the axial direction.

2. The bearing condition detection device according to claim 1, wherein the sensor is arranged so that the sensor element has maximum sensitivity to at least one of a magnetic field and an electric field caused by a current flowing radially through the bearing.

3. The bearing condition detection device according to claim 1, wherein the sensor is also disposed opposite the outer circumferential surface of the shaft.

4. The bearing condition detection device according to claim 3, wherein the sensor is positioned so that the second sensor element has maximum sensitivity to at least one of a magnetic field and an electric field caused by a current flowing axially through the shaft.

5. The bearing condition detection device according to claim 1, wherein the sensor has a function of detecting a rotation angle of the rotor. 　 the sensors are provided corresponding to two bearings that support the shaft, a propagation path determination unit that determines a propagation path of the axial current in accordance with the direction of the axial current in each of the two bearings detected by the axial current detection unit; The bearing condition detection device according to any one of claims 1 to 5, further comprising: 　 a voltage sensor for measuring a voltage between the shaft and a housing of the rotating electric machine that holds the bearing; 7. The bearing condition detection device according to claim 1, wherein the axial current detection unit detects the axial current flowing through the bearing based on a signal from the sensor and a signal from the voltage sensor. 　 The rotor, a stator arranged concentrically with and spaced apart from the outer circumferential surface of the rotor; and a housing that holds the bearing and the stator from the outside in the radial direction and accommodates the stator and the rotor therein; A rotating electrical machine equipped with the bearing condition detection device according to any one of claims 1 to 7. 　 an end face of the bearing facing the sensor is covered with a conductive seal plate for protecting the lubricant filled between the inner ring and the outer ring; 9. The rotating electric machine according to claim 8, wherein the sealing plate is insulated from one of the inner ring and the outer ring, and has an opening in a region facing a detection surface of the sensor. 　 a step of disposing a sensor for measuring at least one of a magnetic field and an electric field so as to face at least one of both end faces in an axial direction of a bearing that supports a rotor shaft of a rotating electric machine; detecting an axial current flowing in a radial direction through the bearing based on a signal from the sensor; A bearing condition detection method comprising:

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