Many electric vehicles, including battery electric vehicles, plug-in hybrid electric vehicles, and hybrid electric vehicles, are propelled by a drive unit that includes an electric motor, a power electronics module, and a transmission. Electric motors sometimes include alternating current, three-phase traction motors. However, batteries provide direct current, which is converted to alternating current using an inverter in the power electronic module. The inverter may induce a voltage on the motor shaft and create a parasitic current in the motor bearings. The motor bearings can be comprised of inner and outer bearing raceways and cylindrical or spherical rolling elements. The lubrication fluid film which surrounds the bearing elements may function as an insulator, provided the breakdown voltage of the lubricant is not exceeded. If the lubricant breakdown voltage is exceeded, the hydrodynamic lubrication fluid film is compromised, or arcing happens between the interfaces, pitting in the bearing cages and/balls may happen as a result, which may and shorten the life of the bearing.
While current lubricating materials achieve their intended purpose, room remains for development of lubricant coatings and the method of applying such lubricant coatings on substrates, particularly for motor bearing applications.
Accordingly to various aspects, the present disclosure relates to a method of 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 including sodium metabisulfite (Na2S2O5), sodium molybdate (Na2MoO4·2H2O), a pH modifier, an anionic surfactant, and water. The method further includes applying a first pulsed direct current through the aqueous electrolyte solution using a first direct current power supply and forming a molybdenum disulfide (MoS2) layer on the surface of the substrate. The polarity of the first pulsed direct current causes the substrate to provide an anode and the electrode to provide a cathode.
In embodiments of the above, the first pulsed direct current is applied at a peak density in the range of 5 milliamps per square centimeter (mA/cm{circumflex over ( )}2) to 50 mA/cm{circumflex over ( )}2 for a time period of 5 minutes to twenty minutes, wherein the pulses cycle in the range of 1 second to 4 second and have a duty cycle in the range of 25 percent to 50 percent of the cycle.
In any of the above embodiments, the method further includes preparing the aqueous electrolyte solution by combining the sodium metabisulfite (Na2S2O5) in the range of 5 percent and 15 percent by weight of the total weight of the aqueous electrolyte solution; the sodium molybdate (Na2MoO4·2H2O) in the range of 3 percent and 10 percent by weight of the total weight of the aqueous electrolyte solution, the pH modifier, and the anionic surfactant with the water.
In embodiments of the above, the method further includes combining the pH modifier to the aqueous electrolyte solution and adjusting the pH of the aqueous electrolyte solution to a pH in the range of 4.0 to 7.0. In further embodiments, citric acid is combined as the pH modifier.
In any of the above embodiments, the method includes combining the anionic surfactant in the range of 5 percent and 15 percent by weight of the total weight of the aqueous electrolyte solution.
In any of the above embodiments, the method further includes applying a second pulsed direct current through the aqueous electrolyte solution. The polarity of the second pulsed direct current causes electrode to provide the anode and the substrate to provide the cathode; and forming a black oxide (Fe3O4) layer on the surface of the substrate prior to applying the first pulsed direct current. In further embodiments, the second pulsed direct current is applied at a peak density in the range of 5 milliamps per square centimeter (mA/cm{circumflex over ( )}2) to 25 mA/cm{circumflex over ( )}2 for a time period of one minute to five minutes, wherein the pulses cycle in the range of 1 second to 4 seconds and have a duty cycle in the range of 25 percent to 50 percent of the cycle.
In any of the above embodiments, the molybdenum disulfide (MoS2) layer is in the range of 0.01 micrometer and 4 micrometers in thickness and the black oxide (Fe3O4) layer is in the range of 0.1 micrometer to 3 micrometers in thickness.
In any of the above embodiments, the sodium metabisulfite (Na2S2O5) present in the range of 8 and 12 percent by weight of the total weight of the aqueous electrolyte solution, the sodium molybdate (Na2MoO4·2H2O) present in the range of 3 percent and 7 percent by weight of the total weight of the aqueous electrolyte solution, citric acid as the pH modifier present in the range of 1 percent and 3 percent by weight of the total weight of the aqueous electrolyte solution, TEEPOL 601 S as the anionic surfactant present in the range of 8 percent and 12 percent by weight of the total weight of the solution, and the water.
In any of the above embodiments, immersing the substrate includes immersing at least one surface of a bearing. In further embodiments, the bearing is a ball bearing. In alternative further embodiments, the bearing is a journal bearing.
According to various additional aspects, the present disclosure is directed to a method of coating a bearing surface with a lubricant coating. The method includes immersing a bearing including a surface and an electrode in an electrolyte bath. The electrolyte bath includes an aqueous electrolyte solution including sodium metabisulfite (Na2S2O5), sodium molybdate (Na2MoO4·2H2O), a pH modifier, an anionic surfactant, and water. The method also includes applying a first pulsed direct current through the aqueous electrolyte solution using a direct current power supply and forming a molybdenum disulfide (MoS2) layer on the surface of the bearing. The polarity of the first pulsed direct current causes the bearing to provide an anode and the electrode to provide a cathode.
In embodiments of the above, the first pulsed direct current in the range of 5 milliamps per square centimeter (mA/cm{circumflex over ( )}2) to 50 mA/cm{circumflex over ( )}2 for a time period of 5 minutes to twenty minutes, wherein the pulses cycle in the range of 1 second to 4 second and have a duty cycle in the range of 25 percent to 50 percent of the cycle.
In any of the above embodiments, the method also includes applying a second pulsed direct current through the aqueous electrolyte solution and forming a black oxide (Fe3O4) layer on the surface of the substrate prior to applying the first pulsed direct current. The polarity of the second pulsed direct current causes electrode to provide the anode and the substrate to provide the cathode. In further embodiments, the second pulsed direct current comprises applying the second pulsed direct current in the range of 5 milliamps per square centimeter (mA/cm{circumflex over ( )}2) to 25 mA/cm{circumflex over ( )}2 for a time period of 1 minute to five minutes, wherein the pulses cycle in the range of 1 second to 4 seconds and have a duty cycle in the range of 25 percent to 50 percent of the cycle.
In any of the above embodiments, the method further includes preparing the aqueous electrolyte solution by combining the sodium metabisulfite (Na2S2O5) present in the range of 5 percent and 15 percent by weight of the total weight of the aqueous electrolyte solution, the sodium molybdate (Na2MoO4·2H2O) present in the range of 3 percent and 10 percent by weight of the total weight of the aqueous electrolyte solution, citric acid as the pH modifier present in the range of 1 percent and 3 percent by weight of the total weight of the aqueous electrolyte solution, TEEPOL 601 S as the anionic surfactant present in the range of 5 percent and 15 percent by weight of the total weight of the solution, and the water.
According to yet several additional aspects, the present disclosure relates to a vehicle. The vehicle includes an electric drive unit including a battery, a power electronic module connected to the battery, an electric motor connected to the power electronic module, and a transmission connected to the electric motor. The power electronic module also includes an inverter. A motor shaft is connected to the electric motor and a bearing, including a surface, rotatably supports the motor shaft. In addition, a coating including a molybdenum disulfide (MoS2) layer is disposed on the surface of the bearing, wherein the molybdenum disulfide (MoS2) layer is in the range of 0.1 micrometer and 4 micrometers in thickness.
In embodiments of the above, the coating further includes a black oxide (Fe3O4) layer contacting the surface of the bearing and the molybdenum disulfide (MoS2) layer contacts the black oxide (Fe3O4) layer, wherein the black oxide (Fe3O4) layer is in the range of 0.1 micrometers to 3 micrometers in thickness.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding introduction, summary, or the following detailed description. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
In the claims and 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 section in which they appear, i.e. the specification or the claims or the summary, and are not necessarily consistent between the specification, the claims, and the summary. In that sense they are not intended to limit the elements in any way and a “second” element labeled as such in the claim may or may not refer to a “second” element labeled as such in the specification. Instead, the elements are distinguishable by their disposition, description, connections, and function.
As used herein, the term “vehicle” is not limited to automobiles. While the present technology is described primarily herein in connection with motor bearings used in conjunction with electric vehicles, the technology is not limited to electric vehicles or motor bearings. The concepts can be used in a wide variety of applications, such as in connection with components used in motorcycles, mopeds, locomotives, aircraft, marine craft, and other vehicles, as well as in other applications incorporating hydrogen fuel cells and in applications incorporating electric motors. Applications include, for example, components industrial machines and motors, agricultural equipment, compressors, defense equipment, HVAC (heating, ventilation, and air conditioning) systems, residential and commercial power generators, and pumps, where lubrication of the component is desirable.
Reference will now be made in detail to several examples of the disclosure that are illustrated in accompanying drawings. Whenever possible, the same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps. The drawings are in simplified form and are not to precise scale.
The present disclosure relates to molybdenum disulfide (MoS2) dry film lubricant coatings and electrodeposition of molybdenum disulfide (MoS2) dry film lubricant coatings. The lubricant coatings include a layer of molybdenum disulfide (MoS2) deposited on the surfaces of bearings used in a vehicle and, in embodiments, motor bearing used to support the motor shaft in the electric drive unit of electric vehicles. The lubricant coating may be understood herein as a coating that reduces the friction exhibiting by the surfaces of the substrate the coating is applied to.
Reference is made herein to
In embodiments, the method 100 of forming the lubricant coating begins at block 102 with cleaning the substrate. In embodiments, the substrate may be cleaned with an alkaline detergent or a solvent. Examples of suitable alkaline detergents include one or more of tetra potassium pyrophosphate, potassium hydroxide, sodium metasilicate, and sodium tripolyphosphate. Examples of suitable solvents include one or more of a polar protic solvent such as isopropyl alcohol; a polar aprotic solvent 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 trisodium phosphate. The surfaces of the substrate may be immersed or otherwise contacted with the detergent or solvent, which may then be removed, or evaporated from (in the case of the solvent), the surfaces of the substrate.
At block 106, the molybdenum disulfide (MoS2) coating may be applied to the substrate 202. With reference to
The electrolyte bath 206 includes an aqueous electrolyte solution 212. The aqueous electrolyte solution 212 is prepared by combining sodium metabisulfite (Na2S2O5), sodium molybdate (Na2MoO4·2H2O), a pH modifier, an anionic surfactant, and water. In embodiments, the aqueous electrolyte solution 212 consists essentially of, or consists of, the sodium metabisulfite (Na2S2O5), sodium molybdate (Na2MoO4·2H2O), a pH modifier, an anionic surfactant, and water. In embodiments, the sodium metabisulfite is present in the range of 5 percent to 15 percent by weight of the total weight of the aqueous electrolyte solution, including all values and ranges therein, and the sodium molybdate is present in the range of 3 percent and 10 percent by weight of the total weight of the aqueous electrolyte solution, including all values and ranges therein. The pH modifier may be added in an amount sufficient to change the pH to a pH in the range of 4.0 to 7.0 including all values and increments therein. In embodiments, the citric acid is present in the range of 1 percent to 3 percent by weight of the total weight of the aqueous electrolyte solution, including all values and ranges therein. In addition, the anionic surfactant is present in the range of 5 percent and 15 percent by weight of the total weight of the aqueous electrolyte solution, including all values and ranges therein. The remainder of the aqueous electrolyte solution, to total 100% by weight, is water. In any of the above embodiments, water may be present in the range of 66 percent by weight to 80 percent by weight, including all values and ranges therein.
In embodiments, the pH modifier includes, for example, at least one of citric acid HOC(CO2H)(CH2CO2H)2, ascorbic acid (C6H8O6), acetic acid (CH3COOH), tartaric acid (2,3-dihydroxybutanedioic acid), phosphoric acid (H3PO4), and sulfuric acid (H2SO4). In embodiments, the pH modifier includes citric acid. The anionic surfactant includes for example, at least one of: TEEPOL 610 S (available from Sigma Aldrich); 6-chloro-4-oxo-1,4-dihydro-2-quinazolinecarboxylic acid; sodium lauryl sulfate; sodium dodecyl sulfate; sodium laureth sulfate; phosphoric acid tris(1,3-dichloro-2-propyl-d5 ester); and N-Di[(R)-1-phenylethyl]-[(S)-1,1′-spirobiindane-7,7′-diyl]-phosphoramidite. In any of the above embodiments, the anionic surfactant includes TEEPOL 610 S.
In an embodiment of the above, the aqueous electrolyte solution 212 includes sodium metabisulfite present at 8 percent and 12 percent by weight of the aqueous electrolyte solution, including all values and ranges therein such as 10 percent, sodium molybdate present at 3 percent and 7 percent by weight of the aqueous electrolyte solution, including all values and ranges therein such as 5 percent, citric acid present in the range of 1 percent to 3 percent by weight of the aqueous electrolyte solution, including all values and ranges therein, the anionic surfactant present at 8 percent and 12 percent by weight of the aqueous electrolyte solution, including all values and ranges therein, and the remainder being water present at 72 percent by weight of the aqueous electrolyte solution to total 100% by weight. The anionic surfactant being TEEPOL 610 S.
Without being bound to any particular theory,
In optional embodiments of the above where the substrate 202 includes steel or iron, an iron oxide layer of Fe3O4 (commonly referred to as black oxide or magnetite) is applied prior to applying the molybdenum disulfide (MoS2) at block 104. Iron oxide (Fe3O4) may also be found as a mixture of FeO and Fe2O3. The substrate 202 is immersed in the electrolyte bath 206 along with the electrode 204. The electrolyte bath 206 includes the aqueous electrolyte solution 212 according to the embodiments described above. It should be appreciated that it is not necessary to transfer the substrate 202 to a separate electrolyte bath 206 to form the molybdenum disulfide (MoS2) layer as both the black oxide (Fe3O4) layer and the molybdenum disulfide (MoS2) layer may be applied in the same electrolyte bath 206.
The polarity on the electrodes, i.e., the substrate 202 and the electrode 204, is reversed (causing the substrate 202 to provide the cathode and the electrode 204 to provide the anode), and a second pulsed direct current is applied for a time period in the range of 1 minute to 5 minutes. The pulsed current applied is in the range of 5 mA/cm{circumflex over ( )}2 to 25 mA/cm{circumflex over ( )}2, including all values and ranges therein, in 1 second to 4 second cycles having a duty cycle in the range of 25 to 50 percent. Accordingly, the current may be applied for 0.25 seconds to 2 seconds, every 1 second to 4 seconds. A layer of black oxide (Fe3O4) is deposited on the surface of the substrate 202 and then the molybdenum disulfide (MoS2) layer is applied to the black oxide (Fe3O4) layer at block 106. Prior to applying the molybdenum disulfide (MoS2) layer, the polarity to the electrodes is returned so that the substrate 202 is the anode and the electrode 204 becomes the cathode as described above with respect to block 106. Without being bound to any particular theory,
As illustrated in
In embodiments, the thickness of the lubricant coating 500 is in the range of 2 micrometer to 7 micrometers, including all values and ranges therein. The molybdenum disulfide (MoS2) layer 510 exhibits a thickness in the range of 0.1 micrometers to 4 micrometers, including all values and ranges therein. When present, the black oxide (Fe3O4) layer 506 exhibits a thickness in the range of 0.1 micrometer to 3 micrometers, including all values and ranges therein. In addition, in embodiments, the lubricant coating 500 is fully adhered to the substrate surface, as determined by performing tape adhesion testing per ASTM D3359-22, as well as scratch testing and wear testing. No delamination, gross spalling or chipping, or any other method of adhesive failure of the lubricant coating 500 was observed after performing scratch testing and ball-on-disk mini-traction machine (MTM) wear testing using a 3 mm fixed ball-on-disc test at 50 N load at 100 degrees Celsius for a 16 hour run time.
As illustrated in
The lubricant coatings of the present disclosure offer several advantages. These advantages include, for example, lubricating bearing surfaces, which may provide wear resistance, particularly in applications where a lubricant, such as grease or lubricating oil, may not be utilized, during start-stop of bearing motion, and at higher bearing loads. Additional advantages include the promotion of formation of a hydrodynamic lubricant film, when lubricant is present in the bearing, which also increases the minimum breakdown volage at the bearing surface interfaces. Further advantages include electrical insulation characteristics provided by the band gap exhibited by the molybdenum disulfide (MoS2) layer in the lubricant coating. Yet further advantages include the formation of both a black oxide (Fe3O4) layer and a molybdenum disulfide (MoS2) layer in a single aqueous electrolyte bath without having to remove the substrate from the aqueous electrolyte bath between layers.
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 be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.