JP-2026075313-A - Rolling bearings

Abstract

[Problem] To provide a rolling bearing that can suppress ridge marks caused by electrolytic corrosion. [Solution] The rolling bearings 6 and 7 are incorporated into an inverter-controlled motor 1 and have an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and are lubricated with a lubricant, the lubricant comprising a base oil with a relative permittivity higher than 2.5 and a phosphorus-based additive, the base oil being an ester oil, and the phosphorus-based additive being an aliphatic phosphate ester having a linear or branched alkyl group. [Selection Diagram] Figure 1

Inventors

• 葛谷 紘澄

Assignees

• ＮＴＮ株式会社

Dates

Publication Date

20260508

Application Date

20241022

Claims (5)

1. A rolling bearing incorporated into an inverter-controlled device, having an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and lubricated with a lubricant, The rolling bearing is characterized in that the lubricant comprises a base oil with a relative permittivity higher than 2.5 and a phosphorus-based additive.
2. The rolling bearing according to claim 1, characterized in that the base oil is an ester oil.
3. The rolling bearing according to claim 1 or 2, characterized in that the phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group.
4. The rolling bearing according to claim 1 or 2, characterized in that the phosphorus-based additive is an aliphatic phosphate ester having a linear or branched alkyl group, the aliphatic phosphate ester has three alkyl groups, each alkyl group having 2 to 8 carbon atoms, the phosphorus content relative to the total amount of the lubricant is 0.01% by mass or more and less than 2.0% by mass, and the lubricant does not contain a sulfur-based additive.
5. The rolling bearing according to claim 1 or 2, characterized in that the oil film parameter Λ in a steady-state operating condition is greater than 3, and the ratio of the relative permittivity of the base oil to the oil film parameter Λ (relative permittivity / oil film parameter) is 0.4 or more and less than 0.8.

Description

This invention relates to a rolling bearing lubricated with a lubricant, and more particularly to a rolling bearing incorporated into an inverter-controlled device. Rolling bearings are used in fan motors and servo motors used in industrial machinery, as well as in drive motors used in electric vehicles (EVs) and hybrid vehicles. These rolling bearings are equipped with mechanisms that either contain a lubricant or allow lubricant to penetrate the contact points to provide lubrication. In recent years, most motors used in industrial machinery and drive systems are controlled by inverters to improve efficiency. Inverter control adjusts the voltage and frequency input to the motor according to the motor's set rotational speed. As the inverter's switching frequency increases, the frequency of motor shaft voltage generation also increases. As a result, a potential difference can occur between the outer and inner rings and the rolling elements in the rolling bearings incorporated into inverter-driven motors. If this potential difference becomes large enough to exceed the dielectric breakdown voltage of the oil film formed between the raceway rings and rolling elements within the bearing, discharge can occur between the raceway rings and rolling elements, causing electrolytic corrosion inside the bearing. Furthermore, while higher power supply voltages allow for lower currents at the same output, reducing copper losses in cables and inverter elements, the increased potential difference between the shaft potential and ground potential makes dielectric breakdown of the oil film more likely. As this galvanic corrosion progresses, striped, uneven surfaces called ridge marks form on the racing surfaces of the outer and inner rings. These ridge marks can cause noise and vibration in the bearing. Therefore, development is underway to create bearings that suppress the formation of ridge marks on the racing surfaces. For example, Patent Document 1 describes a conductive grease containing a base oil consisting of at least one of perfluoropolyether and fluorosilicone, a thickener such as a fluorine compound, and carbon black. Patent Document 2 describes the provision of a conductive seal as a seal to seal the end of the bearing space. Patent No. 4599769Patent No. 4177057 This is a schematic cross-sectional view of the motor.This is a cross-sectional view of a deep groove ball bearing, which is an example of a rolling bearing of the present invention.This diagram shows the structures of the phosphorus-based and sulfur-based additives used in the example.These are observational photographs of the inner track surface for Reference Examples 1-5.These are photographs of the inner raceway surfaces of Comparative Examples 1 and 2.This is a diagram illustrating the Anderon trial.This graph shows the results of the Anderon trial.This is a schematic diagram of the SRV test machine.This graph shows the changes in the coefficient of friction and electrical resistance values during the SRV test.This graph shows the electrical resistance values for each additive used under different loads.This is a schematic diagram of a device for measuring relative permittivity.These are photographs of the inner ring raceway surfaces of Examples 1 and 2 and Comparative Example 1. The inventors of this invention have diligently studied how to suppress ridge marks caused by electrolytic corrosion in rolling bearings incorporated into inverter-controlled devices. In their studies, they considered that the higher the dielectric breakdown voltage, the more likely ridge marks are to develop. Based on knowledge regarding the relationship between dielectric breakdown voltage and polarity, they focused on the relative permittivity of the base oil and found that ridge marks could be suppressed by using a base oil with a relatively high relative permittivity. Furthermore, they discovered that when phosphorus-based additives, conventionally used as extreme pressure additives, were used, for example, under fluid lubrication conditions (oil film parameter Λ < 3), an insulating film was formed, surprisingly suppressing ridge marks caused by electrolytic corrosion. This invention is based on these findings. The rolling bearing of the present invention will be described with reference to Figure 1. The rolling bearing of the present invention is a rolling bearing incorporated into an inverter-controlled device. Here, inverter control controls the voltage and frequency according to the set rotational speed. As the switching frequency of the inverter increases, the frequency of shaft voltage generation increases accordingly. As a result, in a rolling bearing incorporated into, for example, an inverter-driven motor, a potential difference may occur between the raceways, which can lead to electrolytic corrosion. Examples of inverter-controlled devices include motors, reducers, and transmissions. Figure 1 shows a schematic cross-sectional view of an inverter-controlled motor