Insulation rolling bearing and electric vehicle

Abstract

To provide an insulation rolling bearing which enables a fitting clearance to be set properly between an outer ring and a housing at low costs when used as a bearing supporting a rotary shaft of an electric motor of an electric vehicle.SOLUTION: In an insulation rolling bearing having an insulation layer which covers an outer diameter surface 6 of an outer ring 2 and an axial end surface 7 of the outer ring 2, the insulation layer is a resin film 8 in which a film thickness t of a portion covering the outer diameter surface 6 of the outer ring 2 is 50 μm or thinner.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulating rolling bearing. [Background technology]

[0002] Electric current can pass through the rolling bearings that support the rotating shaft of an electric motor while the bearing is rotating. When this happens, sparks can occur between the outer ring and the rolling elements, or between the inner ring and the rolling elements. These sparks can cause gradual damage to the raceway surface of the outer or inner ring (a phenomenon known as electrolytic corrosion).

[0003] Therefore, to prevent this electrolytic corrosion, insulated rolling bearings are generally used. Widely used insulated rolling bearings include an outer ring, an inner ring arranged coaxially radially inward of the outer ring, a plurality of rolling elements installed between the outer ring and the inner ring, and an insulating layer covering the outer diameter surface and axial end faces of the outer ring. These insulated rolling bearings are broadly divided into those that use a ceramic coating as the insulating layer and those that use a resin coating as the insulating layer.

[0004] An example of an insulated rolling bearing that uses a ceramic coating as an insulating layer is known from Patent Document 1. The insulated rolling bearing of Patent Document 1 has the advantage of being able to achieve high insulation performance because the insulating layer is a ceramic coating, but it has problems with high manufacturing costs, such as the need to form the ceramic coating on the surface of the outer ring by ceramic spraying during bearing manufacture, then fill the numerous pores present in the ceramic coating with a sealing agent such as a synthetic resin, and the need to polish the surface of the ceramic coating. Another problem is that the ceramic coating may crack if subjected to impact.

[0005] Meanwhile, known insulated rolling bearings that use a resin film as an insulating layer are those described in Patent Documents 2 to 7, for example. With the insulated rolling bearings of Patent Documents 2 to 7, during bearing manufacture, the outer ring is set in a resin injection mold and molten resin is injected into the cavity formed between the inner surface of the mold and the surface of the outer ring, thereby forming a resin film on the outer diameter surface and axial end faces of the outer ring (so-called insert molding). This insulated rolling bearing has the advantage of being able to keep manufacturing costs low and not being susceptible to the cracking problem associated with ceramic coatings. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-209562 [Patent Document 2] Japanese Patent Publication No. 2020-063826 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-174303 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-148482 [Patent Document 5] Japanese Patent Application Publication No. 10-37966 [Patent Document 6] Japanese Patent Application Publication No. 9-88972 [Patent Document 7] Japanese Patent Application Publication No. 7-208462 Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, electric vehicles such as EVs (battery electric vehicles) and HEVs (hybrid electric vehicles) use electric motors as the prime movers for vehicle operation. To achieve high efficiency, the electric motors in these electric vehicles are inverter-driven at high frequencies. Therefore, the rolling bearings that support the rotating shafts of the electric motors in electric vehicles are prone to current flowing inside the bearings, which can cause electrolytic corrosion.

[0008] The inventors of the present application considered using an insulated rolling bearing with a resin film as an insulating layer, rather than an insulated rolling bearing with a ceramic film as an insulating layer, as a bearing that supports the rotating shaft of an electric motor for an electric vehicle.As a result of this consideration, it was found that when the insulated rolling bearings (with a resin film as an insulating layer) of Patent Documents 2 to 7 are used as bearings that support the rotating shaft of an electric motor for an electric vehicle, it is difficult to appropriately set the fit clearance between the outer ring and the housing.

[0009] Specifically, the insulated rolling bearings in Patent Documents 2 to 7, which use a resin film as an insulating layer, employ a resin film formed by insert molding, with a thickness of approximately 1 mm. On the other hand, bearings supporting the rotating shaft of an electric motor in an electric vehicle reach high temperatures when the electric motor heats up, but also experience low temperatures when starting the vehicle in winter. Because the linear expansion coefficient of resin is much greater than that of metal, when the insulated rolling bearings in Patent Documents 2 to 7, which have an outer ring whose outer diameter surface is covered with a resin film approximately 1 mm thick, are used as bearings supporting the rotating shaft of an electric motor in an electric vehicle, reducing the fit gap between the outer ring and the housing can result in excessive interference between the outer ring and the housing due to thermal expansion of the resin film at high temperatures. On the other hand, increasing the fit gap between the outer ring and the housing can result in excessive clearance between the outer ring and the housing at low temperatures.

[0010] The problem to be solved by this invention is to provide an insulating rolling bearing that is low cost and allows the fitting clearance between the outer ring and the housing to be appropriately set when used as a bearing to support the rotating shaft of an electric motor for an electric vehicle. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides an insulating rolling bearing having the following configuration. The outer ring and an inner ring arranged coaxially radially inside the outer ring; a plurality of rolling elements incorporated between the outer ring and the inner ring; an insulating layer covering an outer diameter surface of the outer ring and an axial end face of the outer ring, The insulating layer is a resin film having a thickness of 50 μm or less in a portion covering the outer diameter surface of the outer ring.

[0012] This reduces costs because a resin coating is used as the insulating coating rather than a ceramic coating. Furthermore, because the resin coating covering the outer diameter surface of the outer ring is thin, its thickness changes little with temperature changes, preventing excessive interference between the outer ring and housing due to expansion of the resin coating at high temperatures and excessive gaps between the outer ring and housing at low temperatures. Therefore, when used as a bearing supporting the rotating shaft of an electric motor for an electric vehicle, the fit clearance between the outer ring and housing can be appropriately set.

[0013] The resin coating is preferably formed so that the film thickness of the portion covering the outer diameter surface of the outer ring and the film thickness of the portion covering the axial end face of the outer ring are both 10 μm or greater.

[0014] In this way, the resin coating can effectively prevent current from passing through the inside of the bearing while it is rotating, thereby suppressing electrolytic corrosion and enabling the bearing to have a significantly longer lifespan than a normal bearing that does not have a resin coating.

[0015] The outer diameter surface of the outer ring is preferably formed to have a surface roughness of Ra 0.1 μm or more and Ra 0.8 μm or less.

[0016] If the outer diameter surface of the outer ring has a surface roughness of Ra 0.1 μm or more, the adhesive strength of the resin coating to the outer diameter surface of the outer ring can be increased. Furthermore, if the outer diameter surface of the outer ring has a surface roughness of Ra 0.8 μm or less, when a resin coating is formed on the outer diameter surface of the outer ring with a film thickness of 50 μm or less, the surface roughness of the resin coating's surface can be kept low, eliminating the need for additional processing such as polishing of the resin coating's surface, thereby reducing costs.

[0017] The resin film is 6.5×10 -5 It is preferable to form the insulating film from a resin having a linear expansion coefficient of 1 / °C or less.

[0018] In this way, the change in the thickness of the resin film due to temperature changes is small, so when used as a bearing supporting the rotating shaft of an electric motor in an electric vehicle, it is possible to particularly effectively suppress changes in the fitting gap between the outer ring and the housing due to temperature. [Effects of the Invention]

[0019] The insulated rolling bearing of this invention is low-cost because it uses a resin coating instead of a ceramic coating as the insulating coating. Furthermore, because the resin coating covering the outer diameter surface of the outer ring is thin, its thickness changes little with temperature changes, preventing excessive interference between the outer ring and housing due to expansion of the resin coating at high temperatures and excessive gaps between the outer ring and housing at low temperatures. Therefore, when used as a bearing supporting the rotating shaft of an electric motor in an electric vehicle, the fit clearance between the outer ring and housing can be appropriately set. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view showing an insulating rolling bearing according to an embodiment of the present invention; [Figure 2] Enlarged view of the outer diameter surface of the outer ring in Figure 1 DETAILED DESCRIPTION OF THE INVENTION

[0021] Figure 1 shows an insulated rolling bearing 1 according to an embodiment of the present invention. The insulated rolling bearing 1 has an outer ring 2, an inner ring 3 arranged coaxially radially inside the outer ring 2, a plurality of rolling elements 4 assembled between the outer ring 2 and the inner ring 3, a cage 5 that maintains the circumferential spacing between the plurality of rolling elements 4, and a resin coating 8 (insulating layer) that covers the outer diameter surface 6 and axial end face 7 of the outer ring 2.

[0022] An outer ring raceway groove 9 with which the rolling elements 4 roll in contact, and outer ring shoulders 10 located on both axial sides of the outer ring raceway groove 9, are formed on the inner circumference of the outer ring 2. An inner ring raceway groove 11 with which the rolling elements 4 roll in contact, and inner ring shoulders 12 located on both axial sides of the inner ring raceway groove 11, are also formed on the outer circumference of the inner ring 3. The rolling elements 4 are balls in this example. The outer ring raceway groove 9 and the inner ring raceway groove 11 are both grooves with an arc-shaped cross section. The outer ring 2, inner ring 3, and rolling elements 4 are all made of metal (e.g., bearing steel).

[0023] The outer diameter surface 6 of the outer ring 2 is a cylindrical surface with a constant outer diameter that does not change along the axial direction (i.e., a cylindrical surface without grooves). A chamfered portion 13 with an arc-shaped cross section is formed between the outer diameter surface 6 of the outer ring 2 and the axial end face 7 of the outer ring 2. The resin coating 8 is composed of an outer diameter covering portion 8a that covers the outer diameter surface 6 of the outer ring 2, a chamfer covering portion 8b that covers the chamfered portion 13 of the outer ring 2, and an end face covering portion 8c that covers the axial end face 7 of the outer ring 2.

[0024] The outer diameter covering portion 8a is formed to have a film thickness t (see FIG. 2) of 10 μm or more (preferably 15 μm or more) and 50 μm or less. The film thickness t can be set to 20 μm, for example. The end surface covering portion 8c is also formed to have a film thickness of 10 μm or more (preferably 15 μm or more) and 50 μm or less.

[0025] The outer diameter surface 6 (see FIG. 2) of the outer ring 2 is formed so that the surface roughness in the axial direction is Ra 0.1 μm or more and Ra 0.8 μm or less.

[0026] Resin film 8 is 6.5 x 10 -5 The resin is made of a resin having a linear expansion coefficient of 4.0 × 10 / °C or less. Examples of such resins include polyamide-imide resin-based resins (with a linear expansion coefficient of 4.0 × 10 -5 / ℃ or less) or epoxy resin-based resin (linear expansion coefficient of 6.5 × 10 -5 / °C or less) can be used. The resin that constitutes the resin film 8 has a withstand voltage of 0.01 kV / µm or more.

[0027] An example of a method for manufacturing the above-mentioned insulated rolling bearing 1 will be described. First, the outer ring 2 is prepared. Next, a masking member (not shown) is fitted onto the outer ring shoulder 10 on the inner circumference of the outer ring 2 to mask the inner circumference of the outer ring 2. In this state, a resin paint made by dissolving resin in a solvent is sprayed onto the outer ring 2 and dried to form a resin coating on the outer diameter surface 6 and axial end face 7 of the outer ring 2. The resin coating is then baked to form a resin coating 8. After forming the resin coating 8, no additional processing such as polishing is performed on the surface of the resin coating 8. The outer ring 2, inner ring 3, rolling elements 4, and cage 5 are then assembled. Manufacturing the insulated rolling bearing 1 using this method makes it possible to efficiently manufacture the above-mentioned insulated rolling bearing 1 having a resin coating 8 with a thickness of 50 μm or less. As a method for forming a resin coating on the outer diameter surface 6 of the outer ring 2 and the axial end face 7 of the outer ring 2, methods such as brush coating, roller coating, and dipping can be used instead of spray coating of a resin paint in which the resin is dissolved in a solvent.

[0028] The insulating rolling bearing 1 described above is low in cost because it uses a resin film 8 as the insulating layer instead of a ceramic film.

[0029] Furthermore, in this insulated rolling bearing 1, the resin film 8 on the portion (outer diameter coating portion 8a) that coats the outer diameter surface 6 of the outer ring 2 is thin, so that changes in the thickness of the resin film 8 due to temperature changes are small, preventing the expansion of the resin film 8 from causing excessive interference between the outer ring 2 and housing 14 at high temperatures, and preventing the creation of an excessive gap between the outer ring 2 and housing 14 at low temperatures. Therefore, when used as a bearing that supports the rotating shaft 15 of the electric motor of an electric vehicle, the fit gap between the outer ring 2 and housing 14 can be set appropriately.

[0030] Furthermore, in this insulated rolling bearing 1, the portion of the resin coating 8 that coats the outer diameter surface 6 of the outer ring 2 (outer diameter coating portion 8a) and the portion of the resin coating 8 that coats the axial end face 7 of the outer ring 2 (end face coating portion 8c) are both formed to have a thickness of 10 μm or more (preferably 15 μm or more). This resin coating 8 effectively prevents current from passing through the bearing during rotation. This makes it possible to suppress electrolytic corrosion and achieve a significantly longer lifespan than a typical bearing that does not have the resin coating 8. Specifically, when the rotating shaft 15 of an electric motor of an electric vehicle is supported by the insulated rolling bearing 1 and a potential difference (voltage) of 20 V exists between the housing 14 and the rotating shaft 15, it is possible to ensure a lifespan that is at least five times that of a typical bearing that does not have the resin coating 8.

[0031] Furthermore, in this insulated rolling bearing 1, the surface roughness of the outer diameter surface 6 of the outer ring 2 is Ra 0.1 μm or greater, thereby providing high adhesive strength to the resin coating 8 relative to the outer diameter surface 6 of the outer ring 2. Furthermore, because the surface roughness of the outer diameter surface 6 of the outer ring 2 is Ra 0.8 μm or less, when a resin coating 8 is formed on the outer diameter surface 6 of the outer ring 2 at a film thickness of 50 μm or less, the surface roughness of the resin coating 8 is kept low, eliminating the need for additional processing such as polishing on the surface of the resin coating 8 and reducing costs.

[0032] In addition, this insulated rolling bearing 1 has a resistance of 6.5 × 10 -5 Because the resin coating 8 is formed from a resin with a linear expansion coefficient of 1 / °C or less, changes in the thickness of the resin coating 8 due to temperature changes are small. Therefore, when used as a bearing that supports the rotating shaft 15 of the electric motor of an electric vehicle, it is possible to particularly effectively suppress changes in the fit gap between the outer ring 2 and the housing 14 due to temperature changes.

[0033] In the above embodiment, a ball bearing using balls as the rolling elements 4 has been described as an example, but the present invention can also be applied to a roller bearing using rollers as the rolling elements 4.

[0034] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0035] 1. Insulated rolling bearings 2 outer ring 3. Inner circle 4 rolling elements 6 Outer diameter surface 7 Axial end face 8 Resin film 8a Outer diameter coating part 8c End cover part t Film thickness

Claims

1. outer ring (2), an inner ring (3) arranged coaxially on the radially inner side of the outer ring (2); A plurality of balls (4) assembled between the outer ring (2) and the inner ring (3); an insulating layer covering an outer diameter surface (6) of the outer ring (2) and an axial end surface (7) of the outer ring (2), the insulating layer is composed solely of a resin film (8) having a film thickness (t) of 15 μm or more and 50 μm or less in a portion covering the outer diameter surface (6) of the outer ring (2).

2. 2. An insulating rolling bearing according to claim 1, wherein the resin coating (8) is formed so that a film thickness (t) of the portion covering the outer diameter surface (6) of the outer ring (2) and a film thickness of the portion covering the axial end face (7) of the outer ring (2) are 10 μm or more.

3. 3. An insulating rolling bearing according to claim 1, wherein the outer diameter surface (6) of the outer ring (2) is formed to have a surface roughness of Ra 0.1 μm or more and Ra 0.8 μm or less.

4. The resin film (8) is 6.5 × 10 －５ 4. An insulating rolling bearing according to claim 1, which is made of a resin having a linear expansion coefficient of 1 / °C or less.

5. 4. An electric vehicle using the insulating rolling bearing according to claim 1 as a bearing for supporting a rotating shaft of an electric motor for driving the vehicle.

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