Bearing diagnosis method and its device

Abstract

To allow for determining grease deterioration or an abnormality of a bearing regardless of the type of the bearing.SOLUTION: A method of diagnosing a bearing with an inner ring and outer ring is provided, the method comprising measuring electric potential using a probe connected to the inner ring and outer ring, and determining the presence or absence of deterioration of grease sealed in the bearing or an abnormality of the bearing from the electric potential.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for diagnosing a bearing.

Background Art

[0002] In a rotating electric machine, bearings are used to reduce the friction of the rotating shaft and enable smooth rotation. There are sliding bearings and rolling bearings, and rolling bearings are widely used because they are standardized, have excellent compatibility and availability, and are inexpensive. A rolling bearing is composed of raceways (inner ring, outer ring), rolling elements, and a cage, and grease is enclosed to lubricate the rolling elements.

[0003] Since grease deteriorates due to heat, wear powder, or intrusion of water from the outside, it is necessary to periodically replace the grease. The standard for grease replacement is every six months, but depending on the usage environment and conditions, there are cases where the grease does not deteriorate for more than a year. Therefore, users may neglect to replace the grease, which has been a factor leading to failures of rotating electric machines. Thus, it is important to detect the presence or absence of grease deterioration and perform grease replacement at an appropriate time. As an example of a grease deterioration detection technique, Patent Document 1 is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 describes an invention in which a rod on a pillar is provided on the outer ring of a rolling bearing, and the load and displacement amount acting on the rod are measured to evaluate the grease deterioration state.

[0006] However, the method for evaluating the grease deterioration state described in Patent Document 1 requires a space for inserting a rod into the bearing, and the rod is disposed between two rollers of a double-row bearing. However, in the case of a single-row bearing, there is a problem that it is difficult to provide a space for installing the rod.

[0007] An object of the present invention is to determine grease deterioration or bearing abnormality regardless of the type of bearing.

Means for Solving the Problems

[0008] As an example of the present invention, there is provided a method for diagnosing a bearing having an inner ring and an outer ring, wherein a potential difference is measured by a probe connected to the inner ring and the outer ring, and grease deterioration or bearing abnormality encapsulated in the bearing is determined from the potential difference. This is a method for diagnosing a bearing.

Effects of the Invention

[0009] According to the present invention, it is possible to determine grease deterioration or bearing abnormality regardless of the type of bearing.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Example

[0012] FIG. 1 is a partial cross-sectional view of a motor 100 which is an example of a rotating electrical machine. As shown in FIG. 1, the motor 100 includes a stator 11 that receives power supply and generates a rotating magnetic field, a coil end 9, a rotor 12 that rotates by the rotating magnetic field from the stator 11, a cooling fan 14 coaxial with the rotor 12, a housing 10 that supports the stator, an end bracket 3, a shaft 7, a bearing 4, and a fan cover 13 of the cooling fan, and rotates about a rotating shaft. Further, in the following description, the side of the shaft 7 (the right side in FIG. 1) is referred to as the load side, and the side of the fan cover 13 (the left side in FIG. 1) is referred to as the semi-load side.

[0013] FIG. 2 is a cross-sectional view of the grease discharge structure of the motor 100. In FIG. 2, the arrow indicates the flow of the lubricating grease that has been injected. As shown by the solid-line arrow, the grease injected from the grease nipple 2 passes through the grease injection passage 3a provided inside the end bracket 3 and is supplied into the bearing housing composed of the bearing 4 and the end bracket 3. The grease becomes poor in lubrication due to the mixing of wear powder and the intrusion of water from the outside, and becomes waste grease. As shown by the dotted-line arrow, the waste grease accumulates in the grease pocket 15 and is discharged from the grease discharge port 3b provided at the lower part of the end bracket 3.

[0014] FIG. 3 is a partial cross-sectional view of a motor equipped with the bearing diagnostic device 23 of the present embodiment. The bearing diagnostic device 23 includes a potential difference measurement unit 16, an abnormality determination unit 22, and an indicator lamp 21. The rolling bearing includes an outer ring 4a and an inner ring 4b, a plurality of balls or rollers 4c disposed between the outer ring 4a and the inner ring 4b, and a retainer for holding the balls or rollers 4c, as shown in FIG. 3.

[0015] A bearing in which balls are arranged between an outer ring 4a and an inner ring 4b is called a ball bearing, and a bearing in which rollers are arranged is called a roller bearing. Also, a bearing in which only one row of balls or rollers is arranged is called a single-row bearing. A bearing in which two or more rows of balls or rollers are arranged is called a multi-row bearing. Grease is filled in the bearing, and forms an oil film between the outer ring 4a and the inner ring 4b and the balls or rollers 4c, playing a role of preventing direct contact between metal and metal. The bearing outer ring 4a is installed in the end bracket 3, and the bearing inner ring 4b is fixed to the shaft 7.

[0016] The diagnostic device for the bearing of this embodiment measures the potential difference between the bearing outer ring 4a and the inner ring 4b, and judges the deterioration of the grease and the bearing abnormality based on the measurement result. For measuring the potential difference between the bearing outer ring 4a and the inner ring 4b, a potentiometer as a potential difference measuring unit is arranged in the terminal box 1, and two probes 17 are attached to the potentiometer. Of the two probes, one end of one probe 17 is attached to the outer ring 4a, and one end of the other probe is attached to the plate portion 5 for measuring the potential of the inner ring 4b. In this embodiment, as long as it has the bearing outer ring 4a and the inner ring 4b, it is possible to diagnose regardless of whether it is a single row or a multi-row.

[0017] As shown in FIG. 4, the plate portion 5 is, for example, a round plate made of casting with a round hole slightly larger than the outer shape of the shaft in the central portion, and a conductive member 18 is fixed radially in the central hole portion. The conductive member 18 may be, for example, a brush or a spring. By using a brush or a spring as the conductive member 18, the plate portion 5 can be electrically contacted with the rotating shaft. Although the plate portion 5 is fixed to the end bracket 3, an insulating material 19 is provided on the grounding surface with the end bracket 3 as shown in the right figure of FIG. 4, so it is insulated from the end bracket 3.

[0018] This is because the end bracket 3 is electrically connected to the bearing outer ring 4a, and if the plate portion 5 and the end bracket 3 are not insulated, the bearing outer ring 4a and the bearing inner ring 4b will be electrically connected.

[0019] Alternatively, the plate portion 5 may be attached to, for example, the half-load side of the grease cover 6 in the motor 100 without being fixed to the end bracket 3. When the plate portion 5 is fixed to the end bracket 3, it is fixed outside the motor, so it is exposed to water such as rain, making outdoor use impossible. However, by attaching the plate portion 5 to the grease cover 6 in the motor 100, the plate portion 5 is no longer exposed to rainwater, so it can be used even in motors with outdoor specifications.

[0020] The terminal box 1 is a box attached to the housing 10 for waterproofing and protecting the connection point between the motor 100 and the power supply. The potentiometer is fixed to the side of the terminal box so as not to contact the connection point and not to move due to vibration. By fixing the potentiometer inside the terminal box, it is not necessary to change the appearance of the motor 100. For example, when a customer wants to update the motor 100, there is an advantage that it is easy to replace.

[0021] The probe 17 is a device that detects the signal of the object to be measured and transmits it to the measuring instrument. The potential values of the bearing outer ring 4a and the bearing inner ring 4b can be measured by the probe. The probe, the outer ring, and the plate portion 5 are, for example, contact probes that can contact the contact portion of the probe in a state where a certain load is applied by contacting the upper portions of the outer ring and the plate portion 5.

[0022] The potential difference value measured by the potentiometer is transmitted to the abnormality determination unit 22. For example, a PLC (programmable logic controller) may execute the function of the abnormality determination unit 22. Not limited to the PLC, a processor may execute the process of the abnormality determination unit by executing the program stored in the recording unit. When the value of the potential difference transmitted from the potentiometer is below a predetermined threshold value, the abnormality determination unit determines that the grease has deteriorated, and the signal is transmitted to the indicator lamp 21 to turn on the indicator lamp.

[0023] Further, the abnormality determination unit 22 calculates the rate of change of the potential difference transmitted from the potentiometer. When the rate of change of the potential difference exceeds a predetermined threshold value, it is determined that an abnormality has occurred in the bearing, and a signal is transmitted to the indicator lamp 21 to cause the indicator lamp to blink. An example in which the abnormality determination unit 22 calculates the rate of change of the potential difference has been described. However, the potentiometer may calculate the rate of change of the potential difference and transmit the rate of change to the abnormality determination unit 22.

[0024] FIG. 5 shows a conceptual diagram showing the change over time of the potential difference value between the inner and outer rings of the bearing. The vertical axis represents the potential difference V, the horizontal axis represents time, and it is a diagram for explaining grease deterioration determination. As the grease deteriorates, metal wear powder such as iron powder is mixed in, so the electrical resistance of the grease decreases, and the potential difference between the outer ring 4a and the inner ring 4b of the bearing in which the grease is enclosed also decreases.

[0025] Therefore, when the potential difference between the outer ring 4a and the inner ring 4b of the bearing falls below a certain threshold value Vo, by causing the indicator lamp connected to the measuring instrument to light up, it is possible to determine at a glance whether it is time to replace the grease.

[0026] As an example of the method for setting the threshold value Vo representing the deterioration determination criterion, the motor is continuously operated for six months, which is said to be the life of general grease. After six months, the potential difference between the outer and inner rings of the bearing is measured, and this value is set as the threshold value Vo. When the bearing temperature exceeds 75°C, it is said that the life of the grease is halved every time the temperature exceeds 10°C, so it is performed in an environment where the bearing temperature does not exceed 75°C. Also, it is to be carried out in a place with less dust so that the grease deterioration does not progress.

[0027] FIG. 6 shows a conceptual diagram showing the change over time of the rate of change of the potential difference between the inner and outer rings of the bearing. The vertical axis represents the potential difference V, the horizontal axis represents time, and it is a diagram for explaining bearing abnormality determination.

[0028] As shown in FIG. 6, not only when the potential difference between the bearing outer ring 4a and the bearing inner ring 4b falls below the threshold value Vo, but also when the rate of change of the potential difference exceeds a predetermined threshold value V1, it is regarded that an abnormality has occurred in the bearing, and the indicator light is caused to blink. By doing so, not only grease deterioration but also bearing abnormalities can be judged. In FIG. 6, as an example of judging an abnormality in the bearing, the case where the absolute value of the rate of change of the potential difference suddenly increases 61 and exceeds the threshold value V1, or the case where the absolute value of the rate of change of the potential difference suddenly decreases 62 and exceeds the threshold value V1 is shown. Abnormalities occurring in the bearing 4 include flaking (peeling), breakage, scratches, rust, creep, electrolytic corrosion, seizure, etc.

[0029] As an example of a method for setting the rate of change, for example, a bearing in which any of the above abnormalities has occurred and a bearing in which no abnormality has occurred are prepared, and the potential difference between the bearing outer ring 4a and the bearing inner ring 4b is measured. These two bearings are selected to have similar usage times and usage environments in order to match the conditions. From the potential difference values measured for each bearing, the usage time of the bearing, the time since the bearing abnormality occurred, and further the potential difference between the bearing outer ring 4a and the bearing inner ring 4b of an unused bearing, the amount of change in the potential difference with respect to time is calculated.

[0030] FIG. 7 shows a flowchart regarding the processing of the abnormality determination unit of the bearing diagnosis device 23. The abnormality determination unit 22 receives the potential difference signal from the potential difference measurement unit 16, and the processing starts.

[0031] The abnormality determination unit 22 calculates the rate of change of the potential difference and determines whether the rate of change of the potential difference exceeds a predetermined threshold value (step S1).

[0032] When the rate of change of the potential difference exceeds the threshold value (YES in step S1), it is regarded that a bearing abnormality has occurred, and control is performed to blink the indicator light as an output of the diagnosis result (step S2).

[0033] When the rate of change of the potential difference does not exceed the threshold value (NO in the S1 step), the abnormality determination unit 22 determines whether the value of the potential difference is lower than a predetermined threshold value (S3 step). If the rate of change of the potential difference has not been calculated, the S1 step is not executed, and the S3 step is executed.

[0034] When the potential difference is lower than the threshold value (YES in the S3 step), the abnormality determination unit 22 regards it as grease deterioration and controls to turn on the indicator lamp as an output of the diagnosis result (S4 step).

[0035] When the potential difference is not lower than the threshold value (NO in the S3 step), it returns to the S1 step. Grease deterioration and bearing abnormalities are diagnosed in the flow as shown in FIG. 7.

[0036] As another example, in the case of an inverter-driven motor, as shown in FIG. 8, the inverter 20 may be configured to include a diagnosis device 23 having a potential difference measurement unit 16, an abnormality determination unit 22, and an indicator lamp 21. By providing the bearing diagnosis device 23 in the inverter 20, an external measurement unit becomes unnecessary. Also, it is advantageous for selling the motor and inverter as a set.

[0037] According to this embodiment, regardless of the type of bearing, it is possible to determine grease deterioration or bearing abnormality. Also, it becomes possible to perform grease replacement, bearing repair, or replacement at an appropriate time.

Embodiment

[0038] FIG. 9 is a diagram showing an example of a bearing diagnosis device in Embodiment 2. Matters common to Embodiment 1 are omitted from the description.

[0039] As shown in FIG. 9, it is also possible to measure the potential difference between the inner and outer rings of the bearing while the motor is stopped. As shown in FIG. 3, in Embodiment 1, the potential difference between the bearing outer ring 4a and the bearing inner ring 4b is constantly measured during motor operation, whereas in this embodiment, as shown in FIG. 9, the potential difference is measured with the motor stopped.

[0040] The probe that contacts the bearing inner ring 4b is thinner than the grease injection path hole of the end bracket. The probe 17 is inserted along the path. The probe 17 is brought into contact with the bearing inner ring 4b. Also, when measuring in a state where the motor is stopped, the contact portion of the probe may be directly brought into contact with the shaft.

[0041] According to this embodiment, while having the effects of Embodiment 1, since the potential difference measurement unit 16 measures the voltage in a state where the motor is stopped, when a service engineer inspects the motor 100, the deterioration state of the grease can be determined without disassembling the motor 100. Therefore, time and costs can be reduced. Also, by measuring the voltage when the motor is stopped, brushes are not required, so there is an effect of reducing the number of maintenance man-hours.

Explanation of Reference Numerals

[0042] 1... Terminal box, 2... Grease nipple, 3... End bracket, 4... Bearing, 5... Plate portion, 6... Grease cover, 7... Shaft, 8... Grease spatula, 9... Coil end, 10... Housing, 11... Stator, 12... Rotor, 13... Fan cover, 14... Cooling fan, 15... Grease pocket, 16... Potential difference measurement unit, 17... Probe, 18... Conductive member, 19... Insulating material, 20... Inverter, 21... Indicator light, 22... Abnormality determination unit, 23... Diagnostic device for bearing, 100... Motor

Claims

A diagnostic device for a bearing having an inner bearing ring and an outer bearing ring, comprising: a potential difference measurement unit that measures a potential difference based on signals from probes connected to the inner bearing ring and the outer bearing ring; an abnormality determination unit that determines deterioration of grease encapsulated in the bearing or an abnormality of the bearing based on the potential difference; the diagnostic device is configured to diagnose a bearing that supports a shaft of a rotating electric machine; the rotating electric machine has a bearing provided at an end for supporting the shaft and an end bracket for supporting the bearing; the inner bearing ring is fixed to the shaft, and the outer bearing ring is installed in the end bracket; among the probes, a probe connected to the inner bearing ring has a diameter smaller than that of a grease injection passage hole provided in the end bracket and is inserted into the grease injection passage hole to contact the inner bearing ring, a diagnostic device for a bearing.

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