JP2024002477A - Method of diagnosing bearing and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: 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

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a bearing diagnostic method and apparatus.

Bearings are used in rotating electric machines to reduce friction on rotating shafts and allow for smooth rotation. There are two types of bearings: sliding bearings and rolling bearings, but rolling bearings are widely used because they are standardized, highly compatible, readily available, and inexpensive. A rolling bearing is composed of raceway rings (inner ring, outer ring), rolling elements, and a cage, and is filled with grease to lubricate the rolling elements.

Grease deteriorates due to heat, abrasion particles, and water entering from the outside, so it is necessary to periodically replace the grease. The standard for replacing grease is every six months, but depending on the usage environment and usage conditions, there are cases where the grease does not deteriorate for more than a year. Therefore, users sometimes neglect to replace the grease, which can lead to failure of the rotating electric machine. Therefore, it is important to detect the presence or absence of grease deterioration and replace the grease at an appropriate time. Patent Document 1 is disclosed as an example of a grease deterioration detection technique.

Japanese Patent Application Publication No. 2019-20329

Patent Document 1 describes an invention in which a rod on a column is provided on the outer ring of a rolling bearing, and the state of grease deterioration is evaluated by measuring the load and displacement amount acting on the rod.

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 was a problem in that it was difficult to provide a space for installing the rod.

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

An example of the present invention is a method for diagnosing a bearing having an inner ring and an outer ring, in which a potential difference is measured by probes connected to the inner ring and the outer ring, and based on the potential difference, deterioration of the grease sealed in the bearing is determined. This is a bearing diagnostic method for determining an abnormality in the bearing.

According to the present invention, grease deterioration or bearing abnormality can be determined regardless of the type of bearing.

FIG. 3 is a partial cross-sectional view of the electric motor. FIG. 2 is a sectional view of a grease discharge structure of an electric motor. 1 is a diagram showing a bearing diagnostic device according to a first embodiment; FIG. It is a detailed view of a plate part. FIG. 3 is a conceptual diagram showing a change in potential difference value between the inner and outer rings of the bearing over time. FIG. 3 is a conceptual diagram showing a change over time in a rate of change in potential difference between the inner and outer rings of the bearing. 5 is a flowchart regarding bearing diagnosis in Example 1. FIG. FIG. 3 is a diagram showing a case where a bearing diagnostic device is mounted on an inverter. FIG. 7 is a diagram showing a bearing diagnostic device in Example 2.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partial cross-sectional view of an electric motor 100, which is an example of a rotating electric machine. As shown in FIG. 1, the electric 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, and is coaxial with the rotor 12. It is composed of a cooling fan 14, a housing 10 that supports a stator, an end bracket 3, a shaft 7, a bearing 4, and a fan cover 13 for the cooling fan, and rotates on a rotating shaft. In the following description, the shaft 7 side (the right side in FIG. 1) will be referred to as the load side, and the fan cover 13 side (the left side in FIG. 1) will be referred to as the half load side.

FIG. 2 is a cross-sectional view of the grease discharge structure of the electric motor 100. In FIG. 2, arrows indicate the flow of grease. As shown by the solid arrow, grease injected from the grease nipple 2 passes through a grease injection path 3a provided inside the end bracket 3 and is supplied into the bearing box consisting of the bearing 4 and the end bracket 3. Grease becomes waste grease due to poor lubrication due to contamination with wear powder or water intrusion from the outside. As shown by the dotted arrow, 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.

FIG. 3 is a partial sectional view of an electric motor equipped with the bearing diagnostic device 23 of this embodiment. The bearing diagnostic device 23 includes a potential difference measuring section 16, an abnormality determining section 22, and an indicator light 21. As shown in FIG. 3, 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 cage for holding the balls or rollers 4c. We are prepared.

A bearing in which balls are arranged between the outer ring 4a and the inner ring 4b is called a ball bearing, and a bearing in which rollers are arranged is called a roller bearing. A bearing in which only one row of balls or rollers is arranged is called a single-row bearing. A bearing with two or more rows of balls and rollers is called a double-row bearing. Grease is filled in the bearing and forms an oil film between the outer ring 4a, the inner ring 4b, and the balls or rollers 4c, which serves to prevent metals from coming into direct contact. The bearing outer ring 4a is installed inside the end bracket 3, and the bearing inner ring 4b is fixed to the shaft 7.

The bearing diagnostic device of this embodiment measures the potential difference between the bearing outer ring 4a and the inner ring 4b, and determines grease deterioration or bearing abnormality based on the measurement results. In order to measure the potential difference between the bearing outer ring 4a and the inner ring 4b, a potentiometer as a potential difference measuring section is provided in the terminal box 1, and two probes 17 are attached to the potentiometer. One end of one of the two probes 17 is attached to the outer ring 4a, and one end of the other probe 17 is attached to the plate part 5 in order to measure the potential of the inner ring 4b. In this embodiment, as long as the bearing has an outer ring 4a and an inner ring 4b, it is possible to diagnose whether the bearing is a single row or a double row.

As shown in FIG. 4, the plate part 5 is, for example, a round plate made of cast metal, with a round hole slightly larger than the outer diameter of the shaft in the center, and a radial hole is formed in the center hole. A conductive member 18 is fixed to. 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 brought into electrical contact even with a rotating shaft. Although the plate portion 5 is fixed to the end bracket 3, the grounding surface with the end bracket 3 is coated with an insulating material 19 as shown in the right diagram of FIG. ing.

This is because the end bracket 3 is electrically connected to the bearing outer ring 4a, so 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.

Further, the plate portion 5 may not be fixed to the end bracket 3, but may be attached to the half-load side of the grease cover 6 in the electric motor 100, for example. When the plate part 5 is fixed to the end bracket 3, the plate part 5 is fixed to the outside of the motor, so it is exposed to water such as rain, and cannot be used outdoors. However, by attaching the plate part 5 to the grease cover 6 inside the electric motor 100, the plate part 5 is not exposed to rainwater, so that it can be used even with an outdoor electric motor.

The terminal box 1 is a box attached to the housing 10 for waterproofing and protection of the connection point between the electric motor 100 and the power source. Fix the potentiometer to the side of the terminal box so that it does not touch the connection point and will not move due to vibration. By fixing the potentiometer in the terminal box, there is no need to change the appearance of the electric motor 100, which has the advantage of making it easier to replace the electric motor 100, for example, when a customer wants to update the electric motor 100.

The probe 17 is a device that detects a signal from the object to be measured and transmits it to a measuring device, and can measure the potential values of the bearing outer ring 4a and the bearing inner ring 4b. The probe, the outer ring, and the plate part 5 can be brought into contact with the contact part of the probe under a certain degree of load by, for example, contacting the upper part of the outer ring and the plate part 5 with something like a contact probe.

The potential difference value measured by the potentiometer is transmitted to the abnormality determination section 22. For example, a PLC (programmable logic controller) may execute the function of the abnormality determination section 22. The process of the abnormality determination section may be executed by not only the PLC but also a processor by executing a program stored in the recording section. If the value of the potential difference transmitted from the potentiometer falls below a predetermined threshold value, the abnormality determination section determines that the grease has deteriorated, and a signal is transmitted to the indicator light 21 so that the indicator light turns on. .

In addition, the abnormality determination unit 22 calculates the rate of change in the potential difference transmitted from the potentiometer, and if the rate of change in the potential difference exceeds a predetermined threshold value, it determines that an abnormality has occurred in the bearing, and the signal is The signal is transmitted to the indicator light 21 so that the indicator light blinks. An example has been described in which the abnormality determination unit 22 calculates the rate of change in potential difference. However, the present invention is not limited thereto, and the potentiometer may calculate the rate of change in the potential difference and transmit the rate of change to the abnormality determining section 22.

FIG. 5 shows a conceptual diagram showing a change in potential difference value between the inner and outer rings of the bearing over time. The vertical axis shows the potential difference V, the horizontal axis shows time, and is a diagram illustrating 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 bearing outer ring 4a and inner ring 4b in which the grease is sealed also decreases.

Therefore, when the potential difference between the bearing outer ring 4a and the inner ring 4b falls below a certain threshold value Vo, an indicator light connected to the measuring device is turned on, so that it can be determined at a glance whether it is time to replace the grease.

An example of how to set the threshold value Vo, which represents the deterioration criterion, is to operate the motor continuously for 6 months, which is said to be the lifespan of general grease, and measure the potential difference between the bearing outer ring and inner ring after 6 months. Then, this value is set as the threshold value Vo. If the bearing temperature exceeds 75°C, it is said that the life of the grease will be halved for every 10°C it exceeds, so carry out the test in an environment where the bearing temperature does not exceed 75°C. Also, be sure to do this in a place with little dust to prevent grease deterioration.

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

As shown in Fig. 6, a bearing abnormality occurs not only when the potential difference between the bearing outer ring 4a and the bearing inner ring 4b is less than the threshold value Vo, but also when the rate of change of the potential difference exceeds the predetermined threshold value _V1 . It is assumed that this has occurred and the indicator light flashes. By doing so, it is possible to determine not only grease deterioration but also bearing abnormalities. In FIG. 6, the case where the absolute value of the rate of change of the potential difference suddenly increases 61 and exceeds the threshold value V ₁ , or the case where the absolute value of the rate of change of the potential difference rapidly decreases 62 and exceeds the threshold value V ₁ is shown. This is shown as an example of determining a bearing abnormality. Abnormalities occurring in the bearing 4 include flaking, damage, scratches, rust, creep, electrolytic corrosion, and seizure.

As an example of a method of 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 value of the potential difference measured in each bearing, the usage time of the bearing, the time since the bearing abnormality occurred, and the potential difference between the bearing outer ring 4a and the bearing inner ring 4b of the unused bearing, the amount of change in the potential difference with respect to time is determined. Calculate.

FIG. 7 shows a flowchart regarding the processing of the abnormality determination section of the bearing diagnostic device 23. The abnormality determining unit 22 receives the potential difference signal from the potential difference measuring unit 16 and starts processing.

The abnormality determining unit 22 calculates the rate of change in the potential difference, and determines whether the rate of change in the potential difference exceeds a predetermined threshold (step S1).

If the rate of change in the potential difference exceeds the threshold (YES in step S1), it is assumed that a bearing abnormality has occurred, and the indicator light is controlled to blink as an output of the diagnosis result (step S2).

If the rate of change of the potential difference does not exceed the threshold (NO in step S1), the abnormality determining unit 22 determines whether the value of the potential difference is below the predetermined threshold (step S3). If the rate of change in potential difference has not been calculated, step S1 is not executed, but step S3 is executed.

If the potential difference is below the threshold (YES in step S3), the abnormality determining unit 22 regards the grease as having deteriorated, and controls the indicator light to be turned on as an output of the diagnosis result (step S4).

If the potential difference is not below the threshold (NO in step S3), the process returns to step S1. Grease deterioration and bearing abnormalities are diagnosed using the flow shown in Figure 7.

As an example, in the case of an inverter-driven motor, the inverter 20 may include a potential difference measuring section 16, an abnormality determining section 22, and a diagnostic device 23 having an indicator light 21, as shown in FIG. By providing the bearing diagnostic device 23 in the inverter 20, an external measuring section is not required. It is also advantageous for selling the motor and inverter as a set.

According to this embodiment, grease deterioration or bearing abnormality can be determined regardless of the type of bearing. Furthermore, it becomes possible to replace the grease or repair or replace the bearing at an appropriate time.

FIG. 9 is a diagram showing an example of a bearing diagnostic device according to the second embodiment. Descriptions of items common to Example 1 will be omitted.

As shown in FIG. 9, the potential difference between the inner ring and outer ring of the bearing may be measured 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 while the motor is in operation, whereas in this embodiment, as shown in FIG. It measures the potential difference in the current state.

The probe that contacts the bearing inner ring 4b is thinner than the grease injection path hole of the end bracket. A probe 17 is inserted along the path. The probe 17 is brought into contact with the bearing inner ring 4b. Furthermore, when measuring while the motor is stopped, the contact portion of the probe may be brought into direct contact with the shaft.

According to the present embodiment, it has the effect of the first embodiment, and since the potential difference measuring unit 16 measures the voltage while the motor is stopped, when the service engineer inspects the motor 100, the electric motor 100 can be The deterioration state of grease can be determined without disassembling it. Therefore, time and costs can be reduced. Additionally, by measuring the voltage when the motor is stopped, brushes are no longer required, which has the effect of reducing maintenance man-hours.

1...Terminal box, 2...Grease nipple, 3...End bracket, 4...Bearing, 5...Plate part, 6...Grease cover, 7...Shaft, 8...Grease holder, 9...Coil end, 10...Housing, 11...Fixing Child, 12... Rotor, 13... Fan cover, 14... Cooling fan, 15... Grease pocket, 16... Potential difference measuring section, 17... Probe, 18... Conductive member, 19... Insulating material, 20... Inverter, 21... Indicator light , 22... Abnormality judgment unit, 23... Bearing diagnostic device, 100... Electric motor

Claims (12)

A method for diagnosing a bearing having an inner ring and an outer ring, the method comprising:
measuring a potential difference with probes connected to the inner ring and the outer ring;
A bearing diagnostic method for determining deterioration of grease sealed in the bearing or abnormality of the bearing based on the potential difference. The method for diagnosing a bearing according to claim 1,
A bearing diagnostic method that compares the potential difference with a predetermined threshold value and determines that the grease has deteriorated. The method for diagnosing a bearing according to claim 1,
Calculating the rate of change of the potential difference,
A bearing diagnostic method that compares the rate of change with a predetermined threshold value to determine an abnormality in the bearing. The method for diagnosing a bearing according to claim 1,
A bearing diagnosis method that displays the diagnosis results. A diagnostic device for a bearing having an inner ring and an outer ring,
a potential difference measurement unit that measures a potential difference using signals from probes connected to the inner ring and the outer ring;
A bearing diagnostic device comprising: an abnormality determining section that determines deterioration of grease sealed in the bearing or abnormality of the bearing based on the potential difference. The diagnostic device according to claim 5,
The potential difference measuring section includes:
A bearing diagnostic device that determines that the grease has deteriorated when the potential difference falls below a predetermined threshold. The diagnostic device according to claim 5,
The potential difference measuring section includes:
A bearing diagnostic device placed inside the terminal box of a rotating electrical machine. The diagnostic device according to claim 5,
The potential difference measuring section includes:
A diagnostic device for bearings placed inside the inverter that controls rotating electrical machines. The diagnostic device according to claim 5,
The probe is a bearing diagnostic device that is connected to the inner ring via a plate of a rotating electric machine. The diagnostic device according to claim 9,
The plate portion is fixed to an end bracket of a rotating electrical machine via an insulating material. The diagnostic device according to claim 5,
The abnormality determination unit includes:
A bearing diagnostic device that determines that the bearing is abnormal when the rate of change of the potential difference exceeds a predetermined threshold value. A rotating electric machine comprising the bearing diagnostic device according to claim 5.

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