Low Viscosity EV Gear Oil Lubricant Technologies

Abstract Electric vehicle (EV) technology has matured over time, improving in some performance areas against traditional internal combustion engine (ICE) vehicles. Despite advancement, there is considerable opportunities for further improvements, particularly in the broader field of lubrication, including areas like grease. As in any mechanical system, greases and lubricants play a significant role in the component life of EV power plants and drivetrains. Moreover, they can significantly contribute to vehicle efficiency, energy savings, and overall driving experience. Since the lubricants in EVs work under harsh thermal and electrical environments, designing an ideal high performance and stable lubricant can be challenging. This paper evaluates the industry's progress on EV lubrication including analyzing existing lithium-based lubricants and spotlighting advanced material additives such as graphene, boron nitride, or cutting-edge ionic liquids. It also discusses optimizing base stock selection, with a focus on Polyalphaolefin (PAO) molecules and designing various additives to enhanc... Read More

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Modified oil-soluble polyalkylene glycols (PAGs) with low kinematic viscosity at 100° C, low volatility, and high viscosity index, suitable as base oils for lubricants. The PAGs comprise an aryl-polyalkylene glycol monoester compound with a specific molecular structure, providing improved performance characteristics compared to conventional PAGs.

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A lubricating fluid for electric motor systems in hybrid and electric vehicles, comprising a base oil of lubricating viscosity, a high molecular weight succinimide dispersant, an amine salt of a phosphoric acid ester, an ashless dialkyl dithiophosphate, and a sulfur-providing additive. The fluid has a kinematic viscosity of 4.5 cSt or less, 150-250 ppm total phosphorus, and an electrical conductivity of 37 nS/m or less. The succinimide dispersant is derived from a polyisobutylene with a number average molecular weight of 2000 or greater, and is post-treated with a phosphorus and boron containing compound.

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A lubricant composition for electric and hybrid vehicle motors, comprising a base oil blend of polyalkylene glycol (PAG), poly-alpha-olefin (PAO), and ester, with an additive package including a sulfur-based extreme pressure agent. The PAG provides thermal stability and low viscosity, while the PAO and ester enhance solubility and compatibility with the extreme pressure agent. The composition is optimized for electric motor applications, avoiding additives typically used in conventional lubricants that can degrade performance.

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Base oil for automotive transmission and gear systems that provides superior traction and thermal management properties in electric vehicles. The base oil comprises a unique blend of compounds optimized for electric vehicle powertrains, featuring improved oxidation stability, thermal conductivity, and viscosity characteristics. The formulation enables enhanced traction performance in electric vehicles, particularly in the high-temperature regions of the powertrain, while maintaining reliable low-friction operation in the low-temperature conditions of the battery pack and other components.

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A lubricating oil composition for electric vehicle cooling systems, comprising a base oil and a fluorine compound, where the base oil is a mineral oil with a 40°C kinematic viscosity of 1-25 mm²/s, and the fluorine compound content is 3-30% by weight. The composition provides both lubricity and cooling performance, enabling efficient heat management in electric vehicle systems.

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A lubricating fluid for electric motor systems in hybrid and electric vehicles, comprising a lubricating oil and additives, including a succinimide dispersant, a sulfur-providing additive, and a detergent system, that provides improved wear protection, oxidative stability, and electrical conductivity while maintaining low viscosity. The fluid is formulated with a specific combination of additives that balance antiwear, friction, and corrosion performance while minimizing electrical conductivity.

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A transmission fluid composition for hybrid and fully electric vehicles that provides lubrication, cooling, and electrical insulation. The composition comprises a major amount of a lubricating oil basestock and a minor amount of an additive package containing a phosphorus-containing compound, a calcium salicylate detergent, and a non-calcium-salicylate detergent. The additive package enables the fluid to balance competing demands of electrical insulation, wear protection, and low viscosity, while also providing cooling and energy efficiency benefits.

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Lubricating oil composition for electric vehicles comprising a lubricating oil base oil, an extreme pressure agent, and a nitrogen-containing ashless dispersant, suitable for lubricating both electric motors and gear mechanisms in integrated electric vehicle powertrains.

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<div class="section abstract"><div class="htmlview paragraph">Advent of EV powertrain has considerable effect on transmission development activities as competed to regular ICE transmission. Conventional ICE transmission and the transmission for an e-powertrain differ on fundamental level. The conventional transmission has number of gear ratios, shift mechanism which enables the transmission to deliver a smooth power output as per demand from the driver. Whereas the e-powertrain transmission is mostly a single gear ratio transmission (reducer) which primarily depends on speed and torque variation from the motor to cater the driver requirement. Hence, the operating speeds of such e-transmissions can vary from 0 to 20000 rpm in both forward and reverse directions. Such a large speed variation as compared with conventional transmission calls for special attention towards the lubrication of internal components. High speeds and lower oil viscosities tend to disrupt the oil films in between contact surfaces causing metal to metal contact. This situation aggravates the wear and t... Read More

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A lubricating fluid composition for electric drives that prevents corrosion of electrical components while maintaining high efficiency in transmissions. The composition comprises 10-88% by weight of a low-viscosity synthetic oil, 0.1-5% by weight of a borated succinimide dispersant, 0.1-5% by weight of a 2,5-alkyl-thiadiazole compound, and 0.1-5% by weight of a phosphorus-containing additive. The composition has a dynamic viscosity of 0.8-4.0 mm2/s at 100°C and is suitable for use in electric motors, transmissions, and battery-operated vehicles.

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Electric vehicles (EVs) have gained increased attention in recent years owing to their excellent performance and emission of less hazardous products to the surroundings. The varied design of EVs compared to the internal combustion engine vehicles has created new requirements in lubricants and fluids for their operation. The increasing electrification of vehicle drivetrains has led to lubricants being in contact with more electrical components, such as motors, sensors, battery modules, and power electronics. This has led to different operating conditions, such as being subjected to an electric field, higher rpm, and higher thermal stress, affecting the electrical properties of lubricants, especially for electrified transmission fluid. The electrical properties of lubricants play a vital role in preventing corona discharge and arc absorbance, which can cause premature failure and electromagnetic interference problems in motors, leading to bearing instability, excessive vibrations, and noise. Understanding the interactions of lubricants with the electric field is crucial for optimizing ... Read More

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EV transmissions operate at high speeds, upto 30,000 rpm. High speed operation puts higher demands on bearings, seals, and gears. Bearings in EV transmissions are prone to electrically induced bearing damage and may exhibit signs of pitting and fluting. Surface-initiated rolling contact fatigue is another common problem gaining increased attention lately. Most EV transmissions require a coupling between an oil-lubricated gearbox to an electrical motor that runs with minimal lubrication at very high rpm. High mechanical and thermal stresses the seals are exposed to under starved lubrication conditions have a detrimental impact on their service life. Hence, proper lubrication is critical. In general, EV transmission fluids call for a somewhat different spectrum of properties compared to conventional ATF. Gear tribology simulations open new ways to the design and optimization of lubrication for EV transmissions. Additionally, such simulations can also provide valuable insights into the effects of different oil properties on cooling and lubrication efficiencies, thereby helping in matchi... Read More

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Extending the driving range of battery-based electric vehicles is one of the many challenges that need to be overcome before mass adaptation by the public. One of the ways to improve the driving range is to make the power unit more efficient. Currently, ultralow viscosity lubricant is used in power units. The fluid was developed for automatic transmissions and, therefore, not optimized for power unit applications. Before developing an optimized fluid, it is critical to understand the lubrication regimes in power units and quantify the amount of boundary, mixed, and hydrodynamic regimes. Once the relative proportions of boundary, mixed, and hydrodynamic regimes are known, lubricant formulators can select appropriate additive components for the reduction of power losses in those regimes while maintaining component durability (mechanical wear, corrosion, material compatibility, etc.) and lubricant life (oxidation). Understanding the lubrication regimes required an evaluation of power unit efficiency using a production unit under a broad range of speeds and torques. The efficiency data w... Read More

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Abstract A renewed interest in elastohydrodynamic lubrication (EHL) phenomena at high speeds, for which thermal effects strongly influence both traction and film thickness, has grown out of the challenges presented by high-speed geared transmissions in electric vehicles. This study uses a new ball-on-disc set-up employing the well-known ultra-thin-film interferometry technique to simultaneously measure EHL film thickness and traction at entrainment speeds up to 20 m/s and slide-roll ratios up to 100%. The effect of fluid composition is examined for Group I, II and III mineral oils, for two polyalphaolefins in Group IV, and for the traction fluid Santotrac 50. The effect of viscosity in the range 4180 mPa.s is investigated by varying bulk fluid temperature. At high speeds, both film thickness and traction are considerably lower than predicted by conventional EHL theory. The contact is seen to be fully-flooded for all conditions tested. The widely-used thermal EHL correction of Gupta is shown to overcorrect for the film thickness reduction even at modest SRRs. Finally, the influence o... Read More

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Lubricating oil composition for electric drive units, comprising a base oil, a phosphite compound, a metal detergent, a viscosity index improver, and an extreme pressure agent, wherein the base oil contains a branched alkyl group with 3-20 carbon atoms, the phosphite compound has a sulfur-containing group, and the extreme pressure agent is a thiadiazole compound. The composition provides balanced scuffing resistance and copper corrosion protection for electric drive units, particularly gearboxes and motors.

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Lubricating oil composition for transmissions that achieves both low viscosity and high gear protection while preventing copper corrosion and maintaining oxidation stability. The composition combines a sulfur-based extreme pressure agent with a phosphorus-based extreme pressure agent, both having specific molecular structures, to create a protective oil film on metal surfaces. This film suppresses metal-to-metal contact and solid phase fusion, preventing gear damage such as scuffing. The composition is suitable for use in transmissions where gear protection is critical, particularly in applications where low viscosity lubricants are required for fuel efficiency.

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<div class="section abstract"><div class="htmlview paragraph">In this study the main focus is on the low temperature behavior and mobility of lubricating greases; a characteristic that has always been challenging for grease formulators. A series of lab-scale polyurea grease samples are prepared, with three different types of low viscosity synthetic base oils (ISO VG 32), and are examined in terms of their low temperature behavior as potential lubricants for electric motor bearings of electric vehicles (EVs) and hybrid electric vehicles (HEVs). The cold flow properties are analyzed by utilizing a Low Temperature Flow Tester following the DIN 51805-2 (Determination of flow pressure of lubricating greases according to Kesternich method) standard. The test matrix includes the cold flow pressure assessment at various temperatures ranging from -0<sup>o</sup>C to -40<sup>o</sup>C, whereas those measurements are also repeated after various relaxation periods - at selected temperatures - from 4h up to 8h before the actual determination. By employing this mo... Read More

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The development of suitable fluids, including lubricants or coolants, for electric vehicles (EVs) requires large efforts on their formulation, characterization, and performance testing. An important property for these fluids is dielectric strength or breakdown voltage (BDV), which is expected to be as high as possible at wide temperature range. Short circuits and bearing currents are highly undesirable phenomena which are known to cause inefficiencies and potential failure or wear of electromechanical hardware if BDV magnitude is not adequate. In modern EVs, the typical fluids comprise lubricants (for bearings and gears in the driveline) such as automatic transmission fluids (ATFs) and low-viscosity gear oils, and coolants (for thermal management in the battery pack and power electronics), namely, ethylene-glycols and dielectric oils. Although these fluids are reported to have acceptable BDV at room temperature (according to ASTM D877 and/or D1816 standard methods) for electric equipment, BDV is likely to be altered when temperature changes occur. The information of BDV at room (20-3... Read More

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Lubricating oil composition for electric drive units, comprising a base oil, a phosphite with a sulfur-containing group, a thiadiazole compound, and a benzotriazole compound, with specific mass ratios of these components that balance scuffing resistance and copper corrosion protection.

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