Electrodeposition of molybdenum disulfide dry film lubricant coatings

Abstract

A method of forming a lubricant coating, a method of coating a bearing surface with a lubricant coating, and a vehicle including a bearing including a lubricant coating are provided. A substrate, such as a bearing, including a surface and an electrode is impregnated in an electrolyte bath. The electrolyte bath comprises an electrolyte aqueous solution, and the electrolyte aqueous solution comprises sodium pyrosulfite (Na2S2O5), sodium molybdate (Na2MoO4. 2H2O), a pH regulator, an anionic surfactant and water. Applying a first pulsed direct current through the aqueous electrolyte solution using a direct current power source, and forming a molybdenum disulfide (MoS2) layer on the surface of the substrate.

Description

Technical Field

[0001] The present disclosure belongs to the field of coatings, and more particularly to a method of forming a lubricant coating, a method of coating a bearing surface with a lubricant coating, and a vehicle having a bearing including the lubricant coating. Background Art

[0002] Many electric vehicles (including battery electric vehicles, plug-in hybrid vehicles and hybrid vehicles) are driven by a drive unit including an electric motor, a power electronics module and a transmission. The electric motor sometimes includes an AC three-phase traction motor. However, the battery provides a DC current, wherein the DC current is converted into an AC current using an inverter in the power electronics module. The inverter can induce a voltage on the motor shaft and generate parasitic currents in the motor bearings. The motor bearings can be composed of inner and outer bearing raceways and cylindrical or spherical rolling elements. The lubricating film surrounding the bearing elements can act as an insulator, provided that the breakdown voltage of the lubricant is not exceeded. If the lubricant breakdown voltage is exceeded, the hydrodynamic lubricating film can be damaged or arcing can occur between interfaces, as a result of which pitting can occur in the bearing cage and / or the balls, which can shorten the life of the bearing.

[0003] While current lubricating materials achieve their intended purpose, there remains room for development in lubricant coatings and methods of applying such lubricant coatings to substrates, particularly for motor bearing applications. Summary of the invention

[0004] According to various aspects, the present disclosure relates to a method for forming a lubricant coating. The method includes: immersing a substrate including a surface and an electrode in an electrolyte bath. The electrolyte bath includes an aqueous electrolyte solution, the aqueous electrolyte solution including sodium metabisulfite (Na 2 S 2 O 5 ), sodium molybdate (Na 2 MoO 4 ·2H 2 O), a pH adjuster, an anionic surfactant and water. The method further includes: applying a first pulsed direct current through the electrolyte aqueous solution using a first direct current power supply, and forming molybdenum disulfide (MoS 2 The polarity of the first pulsed direct current is such that the substrate acts as an anode and the electrode acts as a cathode.

[0005] In the above embodiment, the temperature is 5 mA / cm 2 ) to 50mA / cm 2A first pulsed direct current is applied for a period of 5 minutes to 20 minutes at a peak density, wherein the period of the pulse is in the range of 1 second to 4 seconds and has a duty cycle in the range of 25% to 50% of the period.

[0006] In any of the above embodiments, the method further comprises: adding 5 wt % to 15 wt % of sodium metabisulfite (Na 2 S 2 O 5 ), 3 wt % to 10 wt % of sodium molybdate (Na 2 MoO 4 ·2H 2 O), a pH adjuster and an anionic surfactant are mixed with water to prepare an electrolyte aqueous solution.

[0007] In the above embodiment, the method further comprises: mixing a pH adjuster with the aqueous electrolyte solution, and adjusting the pH of the aqueous electrolyte solution to a pH of 4.0 to 7.0. In other embodiments, citric acid is mixed as the pH adjuster.

[0008] In any of the above embodiments, the method includes mixing 5 wt % to 15 wt % of anionic surfactant based on the total weight of the aqueous electrolyte solution.

[0009] In any of the above embodiments, the method further comprises: applying a second pulsed direct current through the aqueous electrolyte solution. The polarity of the second pulsed direct current causes the electrode to act as an anode and the substrate to act as a cathode; before applying the first pulsed direct current, a black oxide (Fe 3 O 4 In other embodiments, the temperature is 5 mA / cm 2 ) to 25mA / cm 2 A second pulsed direct current is applied for a period of 1 minute to 5 minutes at a peak density of 100 nm, wherein the period of the pulse is in the range of 1 second to 4 seconds and has a duty cycle in the range of 25% to 50% of the period.

[0010] In any of the above embodiments, molybdenum disulfide (MoS 2 ) layer has a thickness of 0.1 μm to 4 μm, and the black oxide (Fe 3 O 4 ) layer has a thickness of 0.1 μm to 3 μm.

[0011] In any of the above embodiments, sodium metabisulfite (Na 2 S 2 O 5) accounts for 8 wt % to 12 wt % of the total weight of the electrolyte aqueous solution, sodium molybdate (Na 2 MoO 4 ·2H 2 O) accounts for 3 wt % to 7 wt % of the total weight of the electrolyte aqueous solution, citric acid as a pH adjuster accounts for 1 wt % to 3 wt % of the total weight of the electrolyte aqueous solution, and TEEPOL 601S as an anionic surfactant accounts for 8 wt % to 12 wt % of the total weight of the electrolyte aqueous solution.

[0012] In any of the above embodiments, impregnating the substrate comprises: impregnating at least one surface of a bearing. In other embodiments, the bearing is a ball bearing. In alternative other embodiments, the bearing is a journal bearing.

[0013] According to various additional aspects, the present disclosure is directed to a method for coating a bearing surface with a lubricant coating. The method comprises: immersing the bearing including the surface and the electrode in an electrolyte bath. The electrolyte bath comprises an aqueous electrolyte solution, the aqueous electrolyte solution comprising: sodium metabisulfite (Na 2 S 2 O 5 ), sodium molybdate (Na 2 MoO 4 ·2H 2 O), a pH adjuster, an anionic surfactant and water. The method further comprises: applying a first pulsed direct current through the electrolyte aqueous solution using a direct current power supply, and forming molybdenum disulfide (MoS 2 The polarity of the first pulsed direct current is such that the bearing acts as an anode and the electrode acts as a cathode.

[0014] In the above embodiment, the temperature is 5 mA / cm 2 ) to 25mA / cm 2 The first pulsed direct current is applied for a period of 5 minutes to 20 minutes, wherein the period of the pulse is in the range of 1 second to 4 seconds and has a duty cycle in the range of 25% to 50% of the period.

[0015] In any of the above embodiments, the method further comprises: applying a second pulsed direct current through the aqueous electrolyte solution, and forming a black oxide (Fe2O3) on the surface of the substrate before applying the first pulsed direct current. 3 O 4 ) layer. The polarity of the second pulsed DC current is such that the electrode acts as an anode and the substrate acts as a cathode. In other embodiments, the current is applied at 5 mA / cm 2 ) to 25mA / cm 2The second pulsed direct current is applied for a period of 1 minute to 5 minutes, wherein the period of the pulse is in the range of 1 second to 4 seconds and has a duty cycle in the range of 25% to 50% of the period.

[0016] In any of the above embodiments, the method further comprises: adding 5 wt % to 15 wt % of sodium metabisulfite (Na 2 S 2 O 5 ), 3 wt% to 10 wt% of sodium molybdate (Na 2 MoO 4 ·2H 2 O), 1 wt% to 3 wt% of citric acid as a pH adjuster based on the total weight of the electrolyte aqueous solution, 5 wt% to 15 wt% of TEEPOL601S as an anionic surfactant based on the total weight of the electrolyte aqueous solution, and water are mixed to prepare an electrolyte aqueous solution.

[0017] According to several additional aspects, the present disclosure relates to a vehicle. The vehicle includes an electric drive unit, the electric drive unit including a battery, a power electronics module connected to the battery, an electric motor connected to the power electronics module, and a transmission connected to the electric motor. The power electronics module also includes an inverter. A motor shaft is connected to the electric motor and a bearing, and the bearing (including a surface) rotatably supports the motor shaft. In addition, a bearing surface including molybdenum disulfide (MoS 2 ) layer, wherein molybdenum disulfide (MoS 2 ) layer has a thickness of 0.1 μm to 4 μm.

[0018] In the above embodiment, the coating also includes a black oxide (Fe 3 O 4 ) layer, and molybdenum disulfide (MoS 2 ) layer contacts the black oxide (Fe 3 O 4 ) layer, in which the black oxide (Fe 3 O 4 ) layer has a thickness of 0.1 μm to 3 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0020] Figure 1 A molybdenum disulfide (MoS) 2 ) layer and optionally a black oxide layer.

[0021] Figure 2 A method for applying molybdenum disulfide (MoS) on a substrate according to an embodiment of the present disclosure is shown. 2 ) layer and an optional black oxide layer.

[0022] Figure 3 A method for forming one or more layers of molybdenum disulfide (MoS) on a substrate according to an embodiment of the present disclosure is shown. 2 ) layer’s reaction mechanism.

[0023] Figure 4 A reaction mechanism for forming one or more black oxide layers on a substrate according to an embodiment of the present disclosure is shown.

[0024] Figure 5 Molybdenum disulfide (MoS) on a substrate according to an embodiment of the present disclosure is shown. 2 ) and black oxide (Fe 3 O 4 ) Backscattered electron detector scanning electron microscope image of the coating.

[0025] Fig. 6A A bearing according to an embodiment of the present disclosure is shown, the bearing including a molybdenum disulfide (MoS 2 ) lubricant-coated surface.

[0026] Figure 6B The embodiment according to the present disclosure is shown Fig. 6A Cross-sectional view of a bearing.

[0027] Figure 7 A vehicle including an electric drive unit according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0028] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application or use. In addition, it is not intended to be bound by any express or implied theory presented in the foregoing technical field, background technology, summary of the invention or the following detailed description. It should be understood that throughout the drawings, corresponding reference numerals indicate similar or corresponding parts and features.

[0029] In the claims and the specification, certain elements are designated as "first," "second," "third," "fourth," "fifth," "sixth," and "seventh." These are arbitrary designations, intended to be consistent only in the portion in which they appear (i.e., the specification or claims or the Summary of the Invention), and are not necessarily consistent between the specification, the claims, and the Summary of the Invention. In this sense, they are not intended to limit the elements in any way, and a "second" element so marked in a claim may or may not refer to a "second" element so marked in the specification. Instead, these elements can be distinguished by their arrangement, description, connection, and function.

[0030] As used herein, the term "vehicle" is not limited to motor vehicles. Although the present technology is described herein primarily in conjunction with motor bearings used in conjunction with electric vehicles, the technology is not limited to electric vehicles or motor bearings. These concepts can be used in a wide variety of applications, such as for components in motorcycles, mopeds, locomotives, aircraft, ships, and other vehicles, as well as for other applications in conjunction with hydrogen fuel cells and applications in conjunction with electric motors. Applications include, for example, components in industrial machinery and motors, agricultural equipment, compressors, defense equipment, HVAC (heating, ventilation, and air conditioning) systems, residential and commercial generators, and pumps (where lubrication of the components is required).

[0031] Reference will now be made in detail to several examples of the present disclosure illustrated in the accompanying drawings. Whenever possible, the same or similar reference numerals are used in the drawings and the specification to refer to the same or similar parts or steps. The drawings are in simplified form and are not drawn to exact scale.

[0032] The present invention relates to molybdenum disulfide (MoS 2 ) dry film lubricant coating and molybdenum disulfide (MoS 2 ) electrodeposition of a dry film lubricant coating. The lubricant coating includes: molybdenum disulfide (MoS2) deposited on the surface of a bearing used in a vehicle (in some embodiments, a motor bearing for supporting a motor shaft in an electric drive unit of an electric vehicle). 2 A lubricant coating is understood herein to be a coating that reduces the friction exhibited by the surface of the substrate to which the coating is applied.

[0033] References Figure 1 and Figure 2 , Figure 1 and Figure 2 A method for electrodepositing molybdenum disulfide (MoS) on a metal or semiconductor substrate is shown. 2 In some embodiments, in the case of molybdenum disulfide (MoS 2 ) layer before coating the substrate, the black oxide (Fe 3 O 4) layer is applied to the substrate. The substrate constitutes any part of the bearing as further described herein, or other components to which a dry lubricant may be applied. A dry film lubricant may be understood as a solid lubricant. In some embodiments, the substrate comprises at least one of stainless steel (such as 52100 steel), tin-copper alloy, brass, babbitt alloy (such as lead babbitt alloy and tin babbitt alloy), aluminum, and aluminum alloy.

[0034] In some embodiments, the method 100 of forming a lubricant coating begins at frame 102, where a substrate is cleaned. In some embodiments, the substrate may be cleaned with an alkaline detergent or solvent. Examples of suitable alkaline detergents include one or more of tetrapotassium pyrophosphate, potassium hydroxide, sodium metasilicate, and sodium tripolyphosphate. Examples of suitable solvents include: polar protic solvents such as isopropanol; polar aprotic solvents such as acetone, ether, and chloroform; ammonia; ammonium hydroxide; calcium hydroxide; calcium oxide; potassium; potassium hydroxide; potassium carbonate; sodium; sodium carbonate; sodium hydroxide; sodium peroxide; sodium silicate; and one or more of trisodium phosphate. The surface of the substrate may be immersed or otherwise contacted with the detergent or solvent, which may then be removed from the surface of the substrate or evaporated (in the case of a solvent).

[0035] At block 106, molybdenum disulfide (MoS 2 ) coating is applied to the substrate 202. Figure 2 , the substrate 202 is immersed in an electrolyte bath 206 together with the electrode 204. A heater is applied to the electrolyte bath 206, and the electrolyte bath 206 can be maintained at a temperature of 15°C to 40°C (including all values ​​and ranges therein) during the electrodeposition process. In some embodiments, the electrode 204 is formed of an inert electrode material (e.g., stainless steel or platinum-plated titanium). Even when an electric current is applied to the solution, the inert electrode does not react with the aqueous electrolyte solution. A first pulsed direct current is applied through the aqueous electrolyte solution by a DC power supply 208 connected to the substrate 202 and the electrode 204. The polarity of the current on the substrate 202 and the electrode 204 causes the substrate 202 to act as an anode and the electrode 204 to act as a cathode. At 5 milliamperes per square centimeter (mA / cm 2 ) to 50mA / cm 2 The pulse current is applied at a peak current density of 100 Hz to 200 Hz (including all values ​​and ranges therein) with a period of 1 second to 4 seconds and a duty cycle in the range of 25% to 50% of the period. Thus, the current may be applied every 1 second to 4 seconds for 0.25 seconds to 2 seconds. The current is applied for a first total time period of 5 minutes to 20 minutes (including all values ​​and ranges therein). This results in the molybdenum disulfide (MoS 2 ) layer is deposited on the surface of substrate 202. In some embodiments, the layer is molybdenum disulfide (MoS 2) monolayer, which consists of an ordered plane of molybdenum atoms sandwiched between two planes of sulfide ions.

[0036] The electrolyte bath 206 includes an aqueous electrolyte solution 212. The aqueous electrolyte solution 212 is prepared by mixing sodium metabisulfite (Na 2 S 2 O 5 ), sodium molybdate (Na 2 MoO 4 ·2H 2 O), pH adjusting agent, anionic surfactant and water are mixed to prepare. In some embodiments, the electrolyte aqueous solution 212 is essentially composed of the following components, or is composed of the following: sodium metabisulfite (Na 2 S 2 O 5 ), sodium molybdate (Na 2 MoO 4 ·2H 2 O), pH adjusting agent, anionic surfactant and water. In some embodiments, sodium metabisulfite accounts for 5% to 15% by weight of the total weight of the aqueous electrolyte solution (including all values ​​and ranges therein), and sodium molybdate accounts for 3% to 10% by weight of the total weight of the aqueous electrolyte solution (including all values ​​and ranges therein). The pH adjusting agent is added in an amount sufficient to change the pH to a pH of 4.0 to 7.0 (including all values ​​and increments therein). In some embodiments, citric acid accounts for 1% to 3% by weight of the total weight of the aqueous electrolyte solution (including all values ​​and ranges therein). In addition, anionic surfactants account for 5% to 15% by weight of the total weight of the aqueous electrolyte solution (including all values ​​and ranges therein). The remainder of the aqueous electrolyte solution (total 100% by weight) is water. In any of the above embodiments, water accounts for 66% to 80% by weight (including all values ​​and ranges therein).

[0037] In some embodiments, the pH adjuster includes, for example, citric acid HOC (CO 2 H)(CH 2 CO 2 H) 2 , ascorbic acid (C 6 H 8 O 6 ), acetic acid (CH 3 COOH), tartaric acid (2,3-dihydroxysuccinic acid), phosphoric acid (H 3 PO 4 ) and sulfuric acid (H 2 SO 4). In some embodiments, the pH adjuster includes citric acid. The anionic surfactant includes, for example, at least one of the following ingredients: TEEPOL 610S (available from Sigma Aldrich); 6-chloro-4-oxo-1,4-dihydro-2-quinazolinecarboxylic acid; sodium lauryl sulfate; sodium dodecyl sulfate; sodium laureth sulfate; tris(1,3-dichloro-2-propyl-d 5 ester); and N-di[(R)-1-phenylethyl]-[(S)-1,1'-spirobiindane-7,7'-diyl]-phosphoramidite. In any of the above embodiments, the anionic surfactant comprises TEEPOL 610S.

[0038] In the above embodiment, the aqueous electrolyte solution 212 includes: sodium pyrosulfite accounting for 8 wt% to 12 wt% (including all values ​​and ranges therein, such as 10 wt%) of the aqueous electrolyte solution, sodium molybdate accounting for 3 wt% to 7 wt% (including all values ​​and ranges therein, such as 5 wt%) of the aqueous electrolyte solution, citric acid accounting for 1 wt% to 3 wt% (including all values ​​and ranges therein) of the aqueous electrolyte solution, an anionic surfactant accounting for 8 wt% to 12 wt% (including all values ​​and ranges therein) of the aqueous electrolyte solution, and the remainder (which is water) accounting for 72 wt% of the aqueous electrolyte solution (total 100 wt%). The anionic surfactant is TEEPOL 610S.

[0039] Not bound by any particular theory, Figure 3 Shows the use of Figure 2 The electrolyte aqueous solution 212 shown in FIG. 1 and described above forms molybdenum disulfide (MoS) on the surface of the substrate 202. 2 ) layer's reaction mechanism implementation scheme.

[0040] In the above-described alternative embodiment in which the substrate 202 comprises steel or iron, at block 104, before applying molybdenum disulfide (MoS 2 ) layer, apply Fe 3 O 4 Iron oxide (Fe 3 O 4 ) can also be FeO and Fe 2 O 3The substrate 202 is immersed in an electrolyte bath 206 together with the electrode 204. The electrolyte bath 206 contains an aqueous electrolyte solution 212 according to the above-described embodiment. It should be understood that it is not necessary to transfer the substrate 202 to a separate electrolyte bath 206 to form molybdenum disulfide (MoS 2 ) layer, this is because the black oxide (Fe 3 O 4 ) layer and molybdenum disulfide (MoS 2 ) layers can be applied in the same electrolyte bath 206.

[0041] The polarity on the electrodes (i.e., substrate 202 and electrode 204) is reversed (so that substrate 202 acts as a cathode and electrode 204 acts as an anode), and a second pulsed direct current is applied for a period of 1 minute to 5 minutes. The applied pulse current is 5 mA / cm 2 Up to 25mA / cm 2 In the range of (including all values ​​and ranges therein), the period is 1 second to 4 seconds, with a duty cycle in the range of 25% to 50%. Therefore, the current can be applied every 1 second to 4 seconds for 0.25 seconds to 2 seconds. At block 106, the black oxide (Fe 3 O 4 ) layer is deposited on the surface of the substrate 202, and then molybdenum disulfide (MoS 2 ) layer is applied to the black oxide (Fe 3 O 4 ) layer. With respect to block 106, as described above, before applying molybdenum disulfide (MoS 2 ) layer, the polarity of the electrodes is restored so that substrate 202 is the anode and electrode 204 becomes the cathode. Without being bound by any particular theory, Figure 4 The black oxide (Fe 3 O 4 ) layer’s reaction mechanism.

[0042] like Figure 5 As shown, according to Figure 1 and Figure 2 The lubricant coating 500, substrate 202 and molybdenum disulfide (MoS 2 ) layer 508, in some embodiments, the black oxide (Fe 3 O 4 ) layer 506 is formed on the molybdenum disulfide (MoS 2 ) layer 510 and the surface 504 of the substrate 202. In other words, when there is a black oxide (Fe 3 O 4) layer 506, black oxide (Fe 3 O 4 ) layer 506 is formed on the surface 504 of the substrate 202, and the molybdenum disulfide (MoS 2 ) layer 510 is formed on the black oxide (Fe 3 O 4 ) layer 506. In which the black oxide (Fe 3 O 4 ) layer 506, molybdenum disulfide (MoS 2 ) layer 510 is formed on the surface 504 of the substrate 202. Molybdenum disulfide (MoS 2 ) layer 510 and black oxide (Fe 3 O 4 ) layer 506 (when present) both provide a lubricant coating on the surface 504 of the substrate 202. Molybdenum disulfide (MoS 2 ) layer 510 also provides a direct band gap of about 1.8 eV. The band gap of a substance is understood as the distance between the valence band of electrons and the conduction band of electrons. Therefore, molybdenum disulfide (MoS 2 ) layer 510 provides a certain degree of insulation until sufficient energy (or parasitic current) is applied to excite the electrons in the valence band so that the electrons become free electrons and participate in conduction in the conduction band. 2 ) layer 510 provides a semiconductor that can help reduce damage caused by parasitic currents generated, for example, by an electric vehicle (EV) drive unit, as further described herein. In addition, due to the band gap, the lubricant coating 500 can reflect light with wavelengths greater than 688 nm in the visible electromagnetic range.

[0043] In some embodiments, the thickness of the lubricant coating 500 is between 2 microns and 7 microns (including all values ​​and ranges therein). Molybdenum disulfide (MoS 2 ) layer 510 has a thickness of 0.1 micrometer to 4 micrometers (including all values ​​and ranges therein). 3 O 4 ) layer 506, black oxide (Fe 3 O 4) layer 506 has a thickness of 0.1 micron to 3 microns (including all values ​​and ranges therein). In addition, in some embodiments, the lubricant coating 500 is fully adhered to the substrate surface, as determined by performing a tape adhesion test (according to ASTM D3359-22) as well as a scratch test and a wear test. After performing a scratch test and a ball-on-disk micro-traction machine (MTM) wear test (at 100° C., under a load of 50N, using a 3mm fixed ball-on-disk tester), no delamination, severe peeling or chipping of the lubricant coating 500, or any other method of adhesion failure was observed after a run time of 16 hours.

[0044] Fig. 6A and Figure 6B An embodiment of a bearing 600 used as substrate 202 in the above-described method 100 and system 200 is shown. Although a ball bearing 600 is shown, the bearing 600 can be: a ball bearing (including one of a deep groove bearing, an angular contact bearing, a self-aligning bearing, and a thrust ball bearing); a roller bearing (including one of a tapered roller bearing, a spherical roller bearing, a needle bearing, and a cylindrical roller bearing); a journal bearing; and a linear motion bearing (including a sliding bearing). The bearing 600 includes one or more bearing surfaces that contact other moving parts (e.g., a motor shaft), as further described herein.

[0045] like Fig. 6A and Figure 6B As shown, ball bearing 600 includes inner race 602, outer race 604, ball 606, cage 608, and optional shield 610. Inner race 602 includes inner bearing surface 612, and outer race 604 includes outer bearing surface 614, which capture ball 606 with cage 608. Lubricant coating 500 can be applied to at least one surface of bearing 600, and in other embodiments, lubricant coating 500 can be applied to all bearing 600 surfaces (including outer surface 616 of inner race 602 and outer surface 618 of outer race 604, inner bearing surface 612, outer bearing surface 614 and ball 606 surface and optional cage 608 surface). Bearing 600 can also include liquid lubricant, such as grease or oil. In the illustrated aspect, the liquid lubricant is retained between inner bearing surface 612 and outer bearing surface 614, for example, by shield 610 ( Fig. 6A As described above, the use of lubricant coating 500 in addition to the liquid lubricant provides lubrication, particularly when the hydrodynamic lubricating film is compromised, which can occur during start-stop of bearing motion and under higher loads. In addition, black oxide (Fe 3 O 4) layer 506 has oleophilic properties, which also promotes the formation of a hydrodynamic lubricating film between the bearing components. However, it should be understood that there are applications in which no additional lubricant is used.

[0046] Figure 7 An electric vehicle (EV) 700 including an electric drive unit 702 is shown, which includes a motor bearing 600. The electric vehicle 700 may be a battery electric vehicle, a plug-in hybrid vehicle, and a hybrid vehicle. In some embodiments, the electric drive unit 702 may include one or more batteries 704, one or more power electronics modules 708 connected to the one or more batteries 704, one or more electric motors 706 connected to the one or more power electronics modules 708, a motor shaft 716 connected to the one or more electric motors 706, and a transmission 710 connected to the motor shaft 716. The one or more batteries 704 may include, but are not limited to, at least one of a lithium-ion battery, a nickel metal hydride battery, and a solid-state battery. The electric motor 706 may include an AC three-phase traction motor. However, when the battery provides a DC current, an inverter 712 included in the power electronics module 708 must be used to convert the DC current into an AC current. The inverter 712 may induce a voltage on the motor shaft 716 and generate parasitic currents in one or more motor bearings 600, 718 supporting the motor shaft 716. The lubricant present in the bearings 600, 718 may also act as an insulator, provided that the breakdown voltage of the lubricant is not exceeded. The addition of the lubricant coating 500 provides another insulating layer to protect the motor bearings 600, 718 from parasitic currents. The lubricant coating 500 also promotes the formation of a hydrodynamic lubricant film, which increases the minimum breakdown voltage at the bearing surface interface.

[0047] The lubricant coatings of the present disclosure provide several advantages. These advantages include, for example, lubricating the bearing surface, which can provide wear resistance during start-stop of bearing motion and under higher bearing loads, particularly in applications where lubricants such as grease or oil may not be used. Additional advantages include promoting the formation of a hydrodynamic lubricant film (when a lubricant is present in the bearing), which also increases the minimum breakdown voltage at the bearing surface interface. Further advantages include the lubrication of the bearing surface by the molybdenum disulfide (MoS 2 ) layer presents a band gap providing electrical insulation properties. Further advantages include the formation of black oxide (Fe 3 O 4 ) layer and molybdenum disulfide (MoS 2 ) layers without removing the substrate from the aqueous electrolyte bath between layers.

[0048] The description of the present disclosure is merely exemplary in nature, and variations that do not depart from the gist of the present disclosure are intended to fall within the scope of the present disclosure. These variations should not be regarded as departing from the spirit and scope of the present disclosure.

Claims

1. A method for forming a lubricant coating, comprising: Immersing a substrate including a surface and an electrode in an electrolyte bath, wherein the electrolyte bath includes an aqueous electrolyte solution, the aqueous electrolyte solution including sodium pyrosulfite (Na2S2O5), sodium molybdate (Na2MoO4·2H2O), a pH adjuster, an anionic surfactant, and water; applying a first pulsed direct current through the aqueous electrolyte solution using a direct current power source, wherein the polarity of the first pulsed direct current causes the substrate to act as an anode and the electrode to act as a cathode; and A molybdenum disulfide (MoS2) layer is formed on the surface of the substrate.

2. The method according to claim 1, wherein: The method also includes: 2 ) to 50mA / cm 2 The first pulsed direct current is applied for a period of 5 minutes to 20 minutes at a peak current density, wherein the period of the pulse is in the range of 1 second to 4 seconds and has a duty cycle in the range of 25% to 50% of the period.

3. The method according to claim 2, wherein: The method also includes preparing the aqueous electrolyte solution by mixing 5 to 15 weight % of sodium metabisulfite (Na2S2O5) based on the total weight of the aqueous electrolyte solution, 3 to 10 weight % of sodium molybdate (Na2MoO4·2H2O) based on the total weight of the aqueous electrolyte solution, the pH adjuster and the anionic surfactant with the water.

4. The method according to claim 3, wherein: The method further includes mixing the pH adjuster with an aqueous electrolyte solution, and adjusting the pH of the aqueous electrolyte solution to a pH of 4.0 to 7.

0.

5. The method according to claim 4, wherein: The method further includes mixing citric acid as the pH adjuster.

6. The method according to claim 5, wherein: The method further includes mixing 5 wt % to 15 wt % of the anionic surfactant based on the total weight of the aqueous electrolyte solution.

7. The method according to claim 2, wherein: The method also includes: applying a second pulsed direct current through the electrolyte aqueous solution, wherein the polarity of the second pulsed direct current causes the electrode to act as an anode and the substrate to act as a cathode; and, before applying the first pulsed direct current, forming a black oxide (Fe3O4) layer on the surface of the substrate.

8. The method according to claim 7, wherein: Applying the second pulsed direct current includes: applying 5 mA / cm 2 ) to 25mA / cm 2 The second pulsed direct current is applied for a period of 1 minute to 5 minutes at a peak current density, wherein the period of the pulse is in the range of 1 second to 4 seconds and has a duty cycle in the range of 25% to 50% of the period.

9. The method according to claim 1, wherein: The method also includes: preparing the electrolyte aqueous solution by mixing 8 wt % to 12 wt % of sodium metabisulfite (Na2S2O5) based on the total weight of the electrolyte aqueous solution, 3 wt % to 7 wt % of sodium molybdate (Na2MoO4·2H2O) based on the total weight of the electrolyte aqueous solution, 1 wt % to 3 wt % of citric acid as the pH adjuster based on the total weight of the electrolyte aqueous solution, 8 wt % to 12 wt % of TEEPOL 601S as the anionic surfactant based on the total weight of the electrolyte aqueous solution, and water.

10. A vehicle comprising: an electric drive unit comprising a battery, a power electronics module connected to the battery, an electric motor connected to the power electronics module, and a transmission connected to the electric motor; an inverter, said inverter being included in a power electronic module; a motor shaft connected to the electric motor; a bearing rotatably supporting the motor shaft, wherein the bearing comprises a surface; and A coating layer including a molybdenum disulfide (MoS2) layer is disposed on the surface, wherein the thickness of the molybdenum disulfide (MoS2) layer is 0.1 micrometers to 4 micrometers.

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