Plain bearing for the rotating shaft of a vehicle drive motor

Abstract

To provide a sliding bearing that is less susceptible to damage caused by electrical discharge on the rotating shaft and sliding surface. [Solution] The sliding bearing 10 supports the rotating shaft of a vehicle drive motor. The sliding bearing 10 comprises a cylindrical metal base 20 and an insulating layer 30. The metal base 20 includes an inner circumferential surface 21, an outer circumferential surface 22, and two axial end faces 23. The insulating layer 30 covers at least the inner circumferential surface 21 and the two axial end faces 23 of the metal base 20. The maximum thickness of the insulating layer 30 covering the axial end faces 23 of the metal base 20 is 50% or less of the minimum thickness of the insulating layer 30 covering the inner circumferential surface 21 of the metal base 20.

Description

Technical Field

[0001] The present disclosure relates to a sliding bearing that supports the rotating shaft of a vehicle drive motor.

Background Art

[0002] Bearings are used for the rotating shaft of a motor or the like. The motor is used, for example, for driving a vehicle. The motor includes a case, a stator having a coil, a rotor having a magnet, a rotating shaft connected to the rotor, and a bearing provided in the case so as to support the rotating shaft and disposed in a bearing holding hole. Inside the case, the stator is disposed outside the rotating shaft, and the rotor is disposed inside. When the coil of the stator is energized, the coil generates a magnetic field. Due to the interaction between the magnetic field generated by the coil and the magnetic field by the magnet of the rotor, the rotor rotates. Due to the rotation of the rotor, the rotating shaft rotates. The rotational power is output to the outside from the rotating shaft.

[0003] A motor mounted on an electric vehicle is driven by an inverter method as described in, for example, Patent Document 1. In the inverter method, the motor can change the rotational speed of the rotating shaft by changing the frequency of the power supply that energizes the coil.

[0004] For a motor used for driving a vehicle, it is required to increase the frequency of the power supply to improve efficiency. However, when the frequency of the power supply increases, the rotating shaft is likely to be charged. As a result, a large potential difference can occur between the rotating shaft and the case with the bearing intervening. When the bearing is a rolling bearing, discharge due to the potential difference can occur in the lubricating oil between the raceway ring and the rolling elements of the rolling bearing. Due to the discharge, the raceway ring and the rolling elements can be damaged. As a means for preventing damage to the raceway ring and the rolling elements, Patent Document 2 describes that the fitting surface where the raceway ring fits to the rotating shaft or the case is an insulating coating.

[0005] To reduce noise caused by the rotation of a rotating shaft, it is being considered to replace rolling bearings with sliding bearings. In internal combustion engines used to drive vehicles, if the bearing is a sliding bearing, a potential difference can be generated between the rotating shaft and the sliding bearing due to leakage current from the ignition system and electrical equipment of the internal combustion engine, or static electricity due to friction between the rotating shaft and the sliding surface of the sliding bearing, which can cause a discharge. This discharge can damage the sliding surface of the rotating shaft and the sliding bearing. As a means to prevent damage to the sliding surface of the rotating shaft and the sliding bearing, Patent Document 3 describes making the sliding surface of the bearing an insulating resin layer. The resin layer has insulating properties by containing 10 to 40 volume percent of carbon-based particles whose average particle diameter is 15 to 45% of the thickness of the resin layer. In Patent Document 3, damage to the sliding surfaces of the rotating shaft and sliding bearings is avoided by actively inducing minute discharges between the carbon-based particles exposed on the sliding surface and the surface of the rotating shaft, before the potential difference between the resin layer and the rotating shaft becomes large, in a manner that does not cause damage to the sliding surfaces of the rotating shaft or sliding bearings. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-146253 [Patent Document 2] Japanese Patent Publication No. 2023-30949 [Patent Document 3] Japanese Patent Publication No. 2009-92156 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In motors used to drive vehicles, if the bearing is a sliding bearing, the potential difference between the rotating shaft and the case is greater than the potential difference between the rotating shaft and the sliding bearing that occurs in internal combustion engines due to the reasons mentioned above. Even if the sliding bearing described in Patent Document 3 is applied to a motor used to drive a vehicle, it will be damaged, for example, by the resin surrounding the carbon-based particles dissolving. Damage to the sliding surfaces of the rotating shaft and the sliding bearing cannot be sufficiently avoided.

[0008] The purpose of this disclosure is to provide a sliding bearing that is less susceptible to damage caused by electrical discharge on the rotating shaft and sliding surface. [Means for solving the problem]

[0009] The sliding bearing that supports the rotating shaft of the vehicle drive motor in this disclosure is A cylindrical metal substrate including an inner surface, an outer surface, and two axial end faces, It comprises at least an insulating layer covering the inner circumferential surface and the two axial end faces of the metal substrate, The maximum thickness of the insulating layer covering the axial end face of the metal substrate is greater than 0% and 50% or less of the minimum thickness of the insulating layer covering the inner circumferential surface of the metal substrate. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic axial cross-sectional view showing a motor according to one embodiment of the present disclosure. [Figure 2] This is a perspective view of a sliding bearing. [Figure 3] This is a cross-sectional view of a sliding bearing along line A in Figure 2. [Figure 4] Figure 2 shows a cross-section of the sliding bearing along line BB and a plan view observed from the direction along line CC. [Figure 5] This is a cross-sectional view of a sliding bearing along the CC line in Figure 4. [Figure 6] This is a cross-sectional view illustrating the discharge to a sliding bearing in a comparative example. [Figure 7] This figure corresponds to Figure 6 and is a cross-sectional view illustrating a discharge to a sliding bearing in one embodiment. [Figure 8] This is a cross-sectional view of a sliding bearing according to one modified example. [Figure 9] This figure corresponds to Figure 5 and is a cross-sectional view of a sliding bearing relating to another modified example. [Figure 10] This figure corresponds to Figure 5 and is a cross-sectional view of a sliding bearing relating to yet another modified example.

Embodiments for Carrying out the Invention

[0011] One embodiment of the present disclosure and its modifications relate to the following [1] to [4]. [1] A sliding bearing that supports the rotating shaft of a vehicle drive motor, a cylindrical metal substrate including an inner peripheral surface, an outer peripheral surface, and two axial end faces, and an insulating layer covering at least the inner peripheral surface and the two axial end faces of the metal substrate. The maximum thickness of the insulating layer covering the axial end face of the metal substrate is greater than 0% and not more than 50% of the minimum thickness of the insulating layer covering the inner peripheral surface of the metal substrate. A sliding bearing. [2] The metal substrate includes two semi-cylindrical partial metal substrates. The sliding bearing according to [1]. [3] The thickness of the insulating layer covering the axial end face of the metal substrate decreases from the inner peripheral surface to the outer peripheral surface of the metal substrate. The sliding bearing according to [1] or [2]. [4] The axial end face includes an inclined surface inclined with respect to the cylindrical axial direction, The inclined surface of the axial end face is connected to the inner peripheral surface. The sliding bearing according to any one of [1] to [3].

[0012] Hereinafter, an embodiment of the present disclosure and its modifications will be described with reference to the drawings. In the drawings attached to this specification, for the convenience of illustration and easy understanding, the scale, the aspect ratio of the vertical and horizontal dimensions, etc. are appropriately changed and exaggerated from those of the actual object. In some of the drawings, the configurations shown may be omitted in other drawings.

[0013] In this specification, terms specifying shapes, geometric conditions, and their degrees, such as terms like "parallel", "orthogonal", "identical", etc. and values of lengths and angles, etc. are not limited to strict meanings, and are interpreted to include ranges that can be expected to have similar functions.

[0014] In this specification, if there are multiple candidate upper limits and multiple candidate lower limits for a given parameter, the numerical range of that parameter may be a combination of any one candidate upper limit and any one candidate lower limit.

[0015] Figure 1 shows a schematic cross-sectional view of a motor 1 according to one embodiment of the present disclosure. The motor 1 is used, for example, to drive a vehicle. The vehicle is, for example, an electric vehicle. The motor 1 outputs rotation to the outside. As shown in Figure 1, the motor 1 has a case 2, a stator 4, a rotor 5, a rotating shaft 6, and a sliding bearing 10.

[0016] Case 2 houses the other components of the motor 1. Case 2 is provided with a bearing retaining hole 3 into which a sliding bearing 10 is press-fitted. The bearing retaining hole 3 is cylindrical in shape to ensure that the sliding bearing 10 is properly press-fitted. In this embodiment, the inner surface of the bearing retaining hole 3 is not divided into multiple parts but is a single, integrated surface. Case 2 may be composed of multiple parts so that the inner surface of the bearing retaining hole 3 is divided into multiple parts. Case 2 may be provided with an oil passage (not shown) for supplying lubricating oil between the sliding bearing 10 and the rotating shaft 6.

[0017] The stator 4 and rotor 5 generate power for the motor 1. The stator 4 is further away from the rotating shaft 6 than the rotor 5. The stator 4 has a coil 4A. The coil 4A is connected to a power source (not shown). The rotor 5 is connected to the rotating shaft 6. The rotor 5 has magnets.

[0018] The rotating shaft 6 transmits the rotation of the motor 1 to the outside. The rotating shaft 6 extends in the axial direction X and rotates around the axial direction X. The rotating shaft 6 protrudes from the outside of the case 2. The rotating shaft 6 may be connected to a reduction gear (not shown) that amplifies the rotational torque.

[0019] When power is supplied to coil 4A from the power source, coil 4A generates a magnetic field. The interaction between the magnetic field generated by coil 4A and the magnetic field from the magnets on rotor 5 causes rotor 5 to rotate. The rotation of rotor 5 causes the rotating shaft 6 connected to rotor 5 to rotate. In this way, motor 1 outputs the rotation of the rotating shaft 6 as power to the outside.

[0020] The sliding bearing 10 of this embodiment will now be described. The sliding bearing 10 supports the rotating shaft 6 at an appropriate position. The sliding bearing 10 allows the rotating shaft 6 to rotate at an appropriate position. As a result, power loss in the rotation of the rotating shaft 6 is suppressed.

[0021] Figure 2 shows a perspective view of the sliding bearing 10. As shown in Figure 2, the sliding bearing 10 is approximately cylindrical in shape. The rotating shaft 6 passes through the inside of the cylindrical shape of the sliding bearing 10. The axial direction of the cylindrical shape of the sliding bearing 10 coincides with the axial direction X of the rotating shaft 6. The inside of the cylindrical shape of the sliding bearing 10 is the sliding surface that receives the rotating shaft 6. The space between the sliding surface of the sliding bearing 10 and the rotating shaft 6 is filled with lubricating oil (not shown).

[0022] Figure 3 shows a cross-sectional view of the sliding bearing 10 in a direction perpendicular to the axial direction X along line A in Figure 2. As shown in Figure 3, the sliding bearing 10 has a metal substrate 20 and an insulating layer 30.

[0023] The metal substrate 20 is the main body of the sliding bearing 10. The metal substrate 20 is cylindrical in shape. The axial direction of the cylindrical shape coincides with the axial direction X of the rotation axis 6. The metal substrate 20 includes an inner circumferential surface 21, an outer circumferential surface 22, two axial end faces 23, and a circumferential end face 24. The inner circumferential surface 21, the outer circumferential surface 22, and the circumferential end faces 24 extend parallel to the axial direction X. The axial end faces extend in a direction perpendicular to the axial direction X. As shown in Figure 3, the inner circumferential surface 21 and the outer circumferential surface 22 are circumferential in cross-section in a direction perpendicular to the axial direction X. The two axial end faces 23 and the circumferential end face 24 are flat surfaces. As shown in Figure 3, the metal substrate 20 is cylindrical in shape by joining the circumferential end faces 24 of a single metal plate.

[0024] Figure 4 shows a cross-section of the sliding bearing 10 along line BB in Figure 2 and a plan view observed from the direction of line BB. Figure 5 shows a cross-sectional view of the sliding bearing 10 along line CC in Figure 4. The length L1 of the metal substrate 20 along the axial direction X may be constant throughout the circumferential direction. The length L1 of the metal substrate 20 along the axial direction X may be 5 mm or more and 50 mm or less. As shown in Figure 3, the thickness T3 of the metal substrate 20 may be constant throughout the circumferential direction. The thickness T3 of the metal substrate 20 may be 0.8 mm or more and 3 mm or less. The thickness of the metal substrate 20 refers to the length along the normal direction of the inner circumferential surface 21 and the outer circumferential surface 22, and coincides with the length along the radial direction of the cylindrical metal substrate 20.

[0025] As shown in Figures 3, 4, and 5, the metal substrate 20 includes a backing metal layer 25 and a bearing alloy layer 26. The backing metal layer 25 and the bearing alloy layer 26 are each cylindrical in shape. The backing metal layer 25 is positioned radially outward of the bearing alloy layer 26. The inner surface of the backing metal layer 25 and the outer surface of the bearing alloy layer 26 are joined to each other.

[0026] The backing metal layer 25 supports the bearing alloy layer 26. The backing metal layer 25 has excellent strength and is resistant to deformation. The backing metal layer 25 allows the overall thickness of the metal substrate 20 to be reduced while maintaining strength. As shown in Figure 3, the thickness of the backing metal layer 25 may be constant throughout the circumferential direction. The thickness of the backing metal layer 25 may be 0.5 mm or more, or 2.8 mm or less. The backing metal layer 25 may be hypoeutectoid steel or stainless steel containing 0.05 mass% to 0.5 mass% of carbon.

[0027] The bearing alloy layer 26 has functions that should be exhibited as a bearing supporting the rotating shaft 6, such as pressure resistance, wear resistance, heat resistance, high thermal conductivity, and low friction. As shown in Figure 3, the thickness of the bearing alloy layer 26 may be constant throughout the circumferential direction. The thickness T4 of the bearing alloy layer 26 may be 0.1 mm or more, or 0.5 mm or less. The bearing alloy layer 26 may be an aluminum alloy or a copper alloy.

[0028] Beyond the illustrated example, the thickness T3 of the metal substrate 20 and the thickness T4 of the bearing alloy layer 26 do not necessarily have to be constant in the circumferential direction. The thickness T3 of the metal substrate 20 and the thickness T4 of the bearing alloy layer 26 may be maximum at a certain position in the circumferential direction and decrease as one moves toward a position rotated 180° circumferentially from that position.

[0029] The insulating layer 30 protects the metal substrate 20 from unintended current flowing through it. The insulating layer 30 has insulating properties. Insulation is defined as a resistance value of 10 in an environment with a temperature of 5°C to 30°C and a relative humidity of 45 to 75%, using a commercially available insulation resistance meter (for example, MODEL6018 manufactured by Kyoritsu Electrical Instruments Co., Ltd.), with the line terminal connected to the surface of the insulating layer 30 covering the inner circumferential surface 21 of the metal substrate 20 and the ground terminal connected to the outer circumferential surface 22 of the metal substrate 20. 5This means that the resistance is greater than or equal to Ω. The insulating layer 30 covers at least the entire inner circumferential surface 21 and the entire two axial end faces 23 of the metal substrate 20. The insulating layer 30 covering the inner circumferential surface 21 of the metal substrate 20 becomes the sliding surface of the sliding bearing 10. The insulating layer 30 may also cover at least a portion of the outer circumferential surface 22 of the metal substrate 20. If at least a portion of the outer circumferential surface 22 of the metal substrate 20 is not covered by the insulating layer 30, the sliding bearing 10 will be more easily held in the bearing retaining hole 3 by friction between the metal substrate 20 and the inner surface of the case 2 when it is press-fitted into the bearing retaining hole 3 of the case 2.

[0030] The insulating layer 30 is a thin film. The thickness of the insulating layer 30 covering the axial end face 23 is thinner than the thickness of the insulating layer 30 covering the inner circumferential surface 21 of the metal substrate 20. Specifically, the maximum thickness of the insulating layer 30 covering the axial end face 23 of the metal substrate 20 is greater than 0% of the minimum thickness of the insulating layer 30 covering the inner circumferential surface 21, and 50% or less, preferably 30% or less, and more preferably 5% or less. The thickness T1 of the insulating layer 30 covering the inner circumferential surface 21 of the metal substrate 20 may be constant over the entire circumferential direction. The thickness T1 of the insulating layer 30 covering the inner circumferential surface 21 of the metal substrate 20 may be 5 μm or more, or 50 μm or less. The thickness T1 of the insulating layer 30 covering the inner circumferential surface 21 is the length of the insulating layer 30 covering the inner circumferential surface 21 along the direction normal to the inner circumferential surface 21, and coincides with the length of the insulating layer 30 covering the inner circumferential surface 21 along the radial direction. The thickness T2 of the insulating layer 30 covering the axial end face 23 of the metal substrate 20 may be constant throughout the circumferential direction. The thickness T2 of the insulating layer 30 covering the axial end face 23 of the metal substrate 20 may be 2.5 μm or more, or 25 μm or less. The thickness T2 of the insulating layer 30 covering the axial end face 23 is the length of the insulating layer 30 covering the axial end face 23 along the direction normal to the axial end face 23, and the length of the insulating layer 30 covering the axial end face 23 along the axial direction X. Due to manufacturing errors during the formation of the insulating layer 30, a variation of 30% or less in the thickness of the insulating layer 30 is acceptable.

[0031] The insulating layer 30 may be made of resin. The insulating layer 30 may contain one or more of the following: polyether ether ketone (PEEK), polyether ketone (PEK), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide-imide (PAI), polyamide (PA), and epoxy (EP). The insulating layer 30 may contain one or more of the following: a solid lubricant, reinforcing fibers to increase strength, fillers, and colorants. Examples of solid lubricants include graphite, molybdenum sulfide (MoS2), tungsten sulfide (WS2), and hexagonal boron nitride (h-BN). Examples of reinforcing fibers include carbon fibers and metal compound fibers. Examples of fillers include calcium fluoride (CaF2), calcium carbonate (CaCO3), barium sulfate, iron oxide, calcium phosphate, and tin oxide (SnO2).

[0032] The method for positioning the sliding bearing 10 in the bearing retaining hole 3 of the case 2 will now be described. The sliding bearing 10 is press-fitted into the bearing retaining hole 3 of the case 2 with the circumferential end faces 24 of the metal substrate 20 aligned. Before the sliding bearing 10 is press-fitted into the bearing retaining hole 3, the length of the outer circumference of the sliding bearing 10 is slightly greater than the length of the inner circumference of the bearing retaining hole 3. After the sliding bearing 10 is press-fitted into the bearing retaining hole 3, the outer circumference of the sliding bearing 10 and the inner circumference of the bearing retaining hole 3 press against each other. This pressing pressure fixes the sliding bearing 10 in place in the bearing retaining hole 3.

[0033] The rotating shaft 6 is inserted into the cylindrical interior of the sliding bearing 10, which is positioned in the bearing retention hole 3 of case 2. The sliding bearing 10 supports the rotating shaft 6 from the inside, in the appropriate position.

[0034] In the example shown in Figure 1, the motor 1 has two sliding bearings 10, but it is not limited to the illustrated example and may have any number of sliding bearings 10. The case 2 is provided with a number of bearing retaining holes 3 corresponding to the number of sliding bearings 10 that the motor 1 has.

[0035] As mentioned above, motors used to drive vehicles are required to have higher power supply frequencies to improve efficiency. However, when the power supply frequency is high, the rotating shaft becomes more prone to static electricity buildup. As a result, a large potential difference can occur between the rotating shaft and the sliding bearing. If this potential difference exceeds the dielectric breakdown voltage of the lubricating oil supplied between the rotating shaft and the sliding bearing, a discharge occurs from the rotating shaft to the sliding bearing. This discharge can cause damage such as melting of the sliding surfaces of the rotating shaft and the sliding bearing. When the sliding surfaces of the rotating shaft and the sliding bearing are damaged, it becomes difficult for the sliding bearing to support the rotating shaft in the correct position.

[0036] To avoid damage to the sliding surface of a sliding bearing due to electrical discharge, it is conceivable to cover the inner circumferential surface of the metal substrate with an insulating layer. The insulating layer becomes the sliding surface of the sliding bearing. However, if only the inner circumferential surface of the metal substrate is covered with an insulating layer, electrical discharge from the rotating shaft to the axial end face of the metal substrate occurs frequently. This discharge causes the temperature of the sliding bearing to rise. As a result of the sliding bearing becoming hot, damage such as melting of the insulating layer forming the sliding surface may occur due to the heat.

[0037] To avoid discharge on the axial end face of the metal substrate, it is conceivable to cover the axial end face of the metal substrate with an insulating layer. Figure 6 shows a sliding bearing 110 in which the inner circumferential surface 121 and the axial end face 123 of the metal substrate 120 are covered with an insulating layer 130 as a comparative example. To avoid discharge on both the inner circumferential surface 121 and the axial end face 123 of the metal substrate 120, the thickness T2 of the insulating layer 130 covering the axial end face 123 of the metal substrate 120 is approximately the same as the thickness T1 of the insulating layer 130 covering the inner circumferential surface 121 of the metal substrate 120. In such a sliding bearing 110, the dielectric breakdown voltage of the insulating layer 130 covering the inner circumferential surface 121 of the metal substrate 120 is approximately the same as the dielectric breakdown voltage of the insulating layer 130 covering the axial end face 123 of the metal substrate 120. When a potential difference occurs between the rotating shaft 106 and the sliding bearing 110, a discharge E is likely to occur from the rotating shaft 106 to the inner circumferential surface 121, which is at a small distance from the rotating shaft 106. The insulating layer 130 covering the inner circumferential surface 121, which forms the sliding surface, is easily damaged.

[0038] In the sliding bearing 10 of this embodiment, the maximum thickness T2 of the insulating layer 30 covering the axial end face 23 of the metal substrate 20 is 50% or less of the minimum thickness T1 of the insulating layer 30 covering the inner circumferential surface 21 of the metal substrate 20. In such a sliding bearing 10, the dielectric breakdown voltage of the insulating layer 30 covering the axial end face 23 is lower than the dielectric breakdown voltage of the insulating layer 30 covering the inner circumferential surface 21. As shown in Figure 7, when a potential difference occurs between the rotating shaft 6 and the sliding bearing 10, discharge E is likely to occur from the rotating shaft 6 to the axial end face 23, which has a lower dielectric breakdown voltage. Discharge to the inner circumferential surface 21 of the metal substrate 20 is unlikely to occur. The insulating layer 30 covering the inner circumferential surface 21, which forms the sliding surface, is less susceptible to damage from discharge.

[0039] Even if the insulating layer 30 covering the axial end face 23 is damaged by the discharge E, the insulating layer 30 covering the inner circumferential surface 21 that forms the sliding surface remains unaffected. Because the axial end face 23 is covered by the insulating layer 30, discharge from the rotating shaft 6 to the axial end face 23 of the metal substrate 20 does not occur as frequently as the temperature of the sliding bearing 10 would suggest.

[0040] Various modifications may be made to the sliding bearing 10 of the embodiment described above. Several modifications of the sliding bearing 10 will be described below. In each of the modifications described below, explanations common to the embodiment described above may be omitted.

[0041] In the sliding bearing 10 of the above-described embodiment, the metal base 20 is cylindrical in shape by joining the circumferential end faces 24 of a single metal plate. Not limited to the above-described embodiment, the metal base 20 may include two semi-cylindrical partial metal bases 27, as shown in the modified example in Figure 8. The metal base 20 becomes cylindrical by joining the respective circumferential end faces 24 of the two semi-cylindrical partial metal bases 27. The inner circumferential surface 21, outer circumferential surface 22, two axial end faces 23, and circumferential end face 24 of the metal base 20 are formed by the two semi-cylindrical partial metal bases 27. The portion of the inner circumferential surface 21 of the metal base 20 formed by each partial metal base 27 has a single arc shape in a cross-section perpendicular to the axial direction X, but it may have multiple arc shapes.

[0042] The thickness of the partial metal substrate 27 may be constant throughout the circumferential direction. The thickness of the partial metal substrate 27 may be 0.8 mm or more, or 3 mm or less. The thickness of the partial metal substrate 27 does not have to be constant in the circumferential direction. The thickness of the partial metal substrate 27 may be maximum at the center in the circumferential direction and decrease towards the circumferential end face 24. The thickness of the partial metal substrate 27 refers to the length along the radial direction of the semi-cylindrical partial metal substrate 27.

[0043] In the sliding bearing 10 of the above-described embodiment, the thickness T2 of the insulating layer 30 covering the axial end face 23 of the metal substrate 20 is constant throughout the radial direction. As shown in the modified example in Figure 9, the thickness T2 of the insulating layer 30 covering the axial end face 23 of the metal substrate 20 does not have to be constant in the radial direction. More specifically, the thickness T2 of the insulating layer 30 covering the axial end face 23 of the metal substrate 20 may decrease in the radial cross-section from the inner circumferential surface 21 to the outer circumferential surface 22 of the metal substrate 20. In this modified example as well, the maximum thickness of the insulating layer 30 covering the axial end face 23 of the metal substrate 20 is greater than 0% of the minimum thickness of the insulating layer 30 covering the inner circumferential surface 21, and is 50% or less, preferably 30% or less, and more preferably 5% or less.

[0044] In this modified sliding bearing 10, the dielectric breakdown voltage of the insulating layer 30 covering the axial end face 23 of the metal substrate 20 is maximum near the inner circumferential surface 21 and decreases as it approaches the outer circumferential surface 22. Discharge from the rotating shaft 6 to the axial end face 23 of the metal substrate 20 is more likely to occur at a position closer to the outer circumferential surface 22 than to the inner circumferential surface 21 of the axial end face 23. Even if the temperature of the position of the metal substrate 20 near the outer circumferential surface 22 rises due to discharge, the temperature of the inner circumferential surface 21 of the metal substrate 20 does not rise easily. Damage such as melting of the insulating layer 30 covering the inner circumferential surface 21 of the metal substrate 20, which forms the sliding surface, is less likely to occur due to heat. The insulating layer 30 covering the inner circumferential surface 21, which forms the sliding surface, is less susceptible to damage from discharge.

[0045] In the sliding bearing 10 of the above-described embodiment, the axial end face 23 extends in a direction perpendicular to the axial direction X. As shown in the modified example in Figure 10, the axial end face 23 may include an inclined surface 23B that is inclined with respect to the cylindrical axial direction X. In the example shown in Figure 10, the axial end face 23 includes an orthogonal surface 23A that extends in a direction perpendicular to the axial direction X, and an inclined surface 23B that is inclined with respect to the axial direction X. An inclined surface with respect to the axial direction X means that the angle that the direction in which the surface extends makes with respect to the axial direction X is greater than 0° and less than 90°. The angle that the direction in which the inclined surface 23B extends makes with respect to the axial direction X may be 10° or more, or 50° or less.

[0046] The inclined surface 23B is connected to the orthogonal surface 23A. The inclined surface 23B is located closer to the inner circumferential surface 21 than the orthogonal surface 23A. The inclined surface 23B is connected to the inner circumferential surface 21. The orthogonal surface 23A is connected to the outer circumferential surface 22. The inclined surface 23B is a chamfer of the axial end face 23 relative to the inner circumferential surface 21.

[0047] The thickness T2 of the insulating layer 30 covering the axial end face 23 includes the thickness T5 of the insulating layer 30 covering the orthogonal surface 23A and the thickness T6 of the insulating layer 30 covering the inclined surface 23B. In this modified example, the thickness T5 of the insulating layer 30 covering the orthogonal surface 23A is the length of the insulating layer 30 covering the axial end face 23 along the axial direction X, and the thickness T6 of the insulating layer 30 covering the inclined surface 23B is the length along the direction normal to the inclined surface 23B. The maximum thickness of the insulating layer 30 covering the orthogonal surface 23A and the maximum thickness of the insulating layer 30 covering the inclined surface 23B are greater than 0% of the minimum thickness of the insulating layer 30 covering the inner circumferential surface 21, and 50% or less, preferably 30% or less, and more preferably 5% or less.

[0048] In this modified sliding bearing 10, as shown in Figure 10, the surface of the insulating layer 30 covering the inclined surface 23B is also inclined with respect to the axial direction X. The inclined surface 23B makes it easier to insert the rotating shaft 6 into the cylindrical shape of the sliding bearing 10 when the rotating shaft 6 passes through the inside of the cylindrical shape of the sliding bearing 10.

[0049] The example shown in Figure 10 is not limited to the one shown, but another inclined surface may be connected to the outer circumferential surface 22 on the axial end face 23. The inclined surface may be a chamfer of the axial end face 23 relative to the outer circumferential surface 22. The axial end face 23 may include both an inclined surface 23B connected to the inner circumferential surface 21 and an inclined surface connected to the outer circumferential surface 22.

[0050] The embodiments of this disclosure are not limited to the embodiments and their variations described above, but also include various modifications that a person skilled in the art could conceive, and the effects of this disclosure are not limited to the above-described content and its variations. Various additions, changes, and partial deletions are possible, provided that they do not depart from the conceptual idea and spirit of this disclosure derived from the claims and their equivalents. For example, multiple variations can be combined, provided that they do not interfere with each other's conceptual idea and spirit. [Explanation of Symbols]

[0051] 1 motor 2 cases 3 Bearing retaining holes 4 stata 4A coil 5 rotors 6 rotation axes 10 Plain bearings 20 Metal substrate 21 Inner surface 22 Outer surface 23 Axial end face 23A Orthogonal plane 23B Slope 24 Circumferential end face 25. The Underworld 26 Bearing alloy layer 27 Partial metal substrate X-axis direction

Claims

1. A sliding bearing that supports the rotating shaft of a vehicle drive motor, A cylindrical metal substrate including an inner surface, an outer surface, and two axial end faces, It comprises at least an insulating layer covering the inner circumferential surface and the two axial end faces of the metal substrate, A sliding bearing in which the maximum thickness of the insulating layer covering the axial end face of the metal substrate is greater than 0% and less than or equal to 50% of the minimum thickness of the insulating layer covering the inner circumferential surface of the metal substrate.

2. The sliding bearing according to claim 1, wherein the metal substrate includes two semi-cylindrical partial metal substrates.

3. The sliding bearing according to claim 1, wherein the thickness of the insulating layer covering the axial end face of the metal substrate decreases from the inner circumferential surface to the outer circumferential surface of the metal substrate.

4. The axial end face includes an inclined surface that is inclined with respect to the axial direction of the cylindrical shape, The sliding bearing according to claim 1, wherein the inclined surface of the axial end face is connected to the inner circumferential surface.

Images