Synthetic ester transmission fluid composition, method of making and use as an electric vehicle transmission fluid

Abstract

The application belongs to the technical field of transmission fluid, and particularly relates to a synthetic ester transmission fluid composition, a preparation method thereof and application of the synthetic ester transmission fluid as electric vehicle transmission fluid. The synthetic ester transmission fluid composition provided by the application comprises the following components in mass percentage: 1-3% of dispersant, 0.5-1.5% of anti-wear and anti-friction agent, 2-4% of antioxidant, 0.05-0.2% of corrosion inhibitor, and the rest is synthetic ester base oil. The synthetic ester transmission fluid composition provided by the application has extremely low conductivity, high breakdown voltage and excellent heat conduction performance, and also exhibits high initial oxidation temperature and excellent antioxidant capacity, significantly delays the aging process of the oil product, and prolongs the oil change cycle, thereby providing long-term, efficient and reliable lubrication protection for the electric vehicle transmission system, and has important practical significance and application value as electric vehicle transmission fluid.

Description

Technical Field

[0001] This invention belongs to the field of transmission fluid technology, specifically relating to a synthetic ester-based transmission fluid composition, its preparation method, and its application as a transmission fluid for electric vehicles. Background Technology

[0002] With the rapid development of the new energy vehicle industry, pure electric vehicles have fully adopted the "three-electric" architecture centered on power batteries, drive motors, and electronic control systems. Currently, the highly integrated design of drive motors, reducers, and electronic control systems has become the mainstream development trend of electric drive systems in new energy vehicles. This integrated structure significantly improves the power density and operating efficiency of the electric drive system, but it also exposes the electric vehicle's transmission fluid to complex and extreme operating conditions involving high speed, high load, strong electric field, and high temperature coupling for extended periods. Compared to traditional fuel vehicle transmission fluids, electric vehicle-specific transmission fluids not only need to meet the basic lubrication, friction reduction, and protection requirements of gears and bearings, but also need to simultaneously meet stringent electrical performance, thermal stability, thermal conductivity, and anti-aging properties, posing new and stringent technical requirements for the overall performance of transmission fluids.

[0003] In integrated electric drive systems, on the one hand, the high power density operation of the system generates severe local temperature rises, which can easily lead to problems such as high-temperature oxidation, deterioration, increased acid value, and precipitation of the oil, directly affecting the service life of motor coils, insulation materials, and precision transmission components. Therefore, the transmission fluid is required to have excellent thermal oxidation stability and high thermal conductivity. On the other hand, gears are prone to failure problems such as micropitting and surface fatigue wear under ultra-high speed and high contact stress, requiring the transmission fluid to have excellent interfacial film-forming ability and extreme pressure anti-wear protection performance. Most importantly, the continuous strong electric field environment generated by the high-voltage electronic control system imposes strict requirements on the electrical safety of the transmission fluid. Conductivity and breakdown voltage have become core indicators for evaluating the suitability of transmission fluids for electric vehicles. Only by accurately controlling the conductivity of the oil within a safe range and maintaining a sufficiently high breakdown voltage can the risks of leakage and breakdown be avoided, ensuring the stable and reliable operation of the electric drive system.

[0004] Currently, the base oils used in electric drive systems for electric vehicles are mainly divided into three categories: mineral oil, polyalphaolefin (PAO), and synthetic ester oils. Each type of base oil has inherent technical defects, making it difficult to adapt to the harsh operating conditions of the new generation of integrated electric drive systems. Among them, mineral oil has poor high-temperature oxidation resistance, poor low-temperature fluidity, and its electrical properties are easily affected by thermal and electric field fluctuations, making it unsuitable for high-voltage, strong electric field operating environments. Although polyalphaolefin (PAO) synthetic oils have relatively excellent dielectric properties, their non-polar molecular structure limits their ability to dissolve high-performance polar additives, making it difficult to form a stable protective oil film on the surface of metal transmission components. Therefore, it is impossible to achieve synergistic optimization of lubrication and anti-wear performance and electrical safety performance.

[0005] Synthetic ester oils, due to their polar ester groups in their molecular structure, possess significant advantages in lubrication and friction reduction, high-temperature stability, compatibility with component materials, and thermal conductivity. Furthermore, their breakdown voltage under both AC and DC high-voltage environments is superior to that of mineral oils, making them a preferred base oil for high-voltage electric drive transmission fluids. However, synthetic ester oils face a core technical bottleneck in industrial applications: to address gear micro-pitting and high-load wear issues, polar anti-wear and protective additives must be added to the base oil. These polar additives completely disrupt the original charge transport balance of the synthetic ester base oil, inducing directional charge migration under strong electric fields, leading to a surge in oil conductivity and creating serious electrical leakage safety hazards.

[0006] In summary, existing ester-based electric vehicle transmission fluids generally suffer from technical defects such as large fluctuations in dielectric properties under high pressure, the risk of leakage induced by polar additives, insufficient high-temperature thermal oxidation stability, and poor long-term physicochemical stability. They cannot simultaneously meet the synergistic requirements of integrated electric drive systems for oil electrical safety, extreme pressure anti-wear properties, thermal stability, and thermal conductivity, which seriously restricts the stable, safe, and long-term operation of high-pressure, high-speed integrated electric drive systems. Summary of the Invention

[0007] The purpose of this invention is to provide a synthetic ester-based transmission fluid composition, its preparation method, and its application as a transmission fluid for electric vehicles. The synthetic ester-based transmission fluid composition provided by this invention has extremely low electrical conductivity, high breakdown voltage, and excellent thermal conductivity. It also exhibits a high initial oxidation temperature and excellent oxidation resistance, significantly delaying the oil aging process and extending the oil change interval. This provides long-lasting, efficient, and reliable lubrication protection for the transmission system of electric vehicles, and has significant practical significance and application value as a transmission fluid for electric vehicles.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a synthetic ester-based transmission fluid composition comprising the following components in weight percentages: 1-3% dispersant, 0.5-1.5% anti-wear and friction-reducing agent, 2-4% antioxidant, 0.05-0.2% corrosion inhibitor, and the balance being synthetic ester base oil; wherein the antioxidant comprises liquid octylbutyldiphenylamine and N-phenyl-α-naphthylamine, and the synthetic ester base oil comprises one or more of the following: di(fatty alcohol) adipic acid ester with the structure shown in Formula I, trimethylolpropane fatty acid ester with the structure shown in Formula II, and pentaerythritol fatty acid ester with the structure shown in Formula III; Formula I, Formula II Equation III, where R1, R2, R3, and R4 are independently C4-C 14 Alkyl groups.

[0009] Preferably, the dispersant includes one or more of monoalkenyl succinimide, dienyl succinimide, and polyisobutylene succinimide.

[0010] Preferably, the anti-wear and friction-reducing agent comprises one or more of ammonium phosphate salt, tricresyl phosphate, octadecyl phosphate, and zinc diisooctyl dithiophosphate.

[0011] Preferably, the corrosion inhibitor comprises one or more of benzotriazole derivatives, thiadiazole derivatives, and dodecenylsuccinic acid.

[0012] Preferably, the corrosion inhibitor comprises one or more of 1H-benzotriazol-1-yl-N,N-di(2-ethylhexyl)-4-methylmethylamine, 2,5-bis(octyldithio)thiadiazole, and dodecenylsuccinic acid.

[0013] Preferably, R1, R2, R3, and R4 are independently C6-C. 10 Alkyl groups.

[0014] Preferably, the synthetic ester base oil comprises one or more of di(tetrazolyl) adipate, trimethylolpropane octyl decanoate, and pentaerythritol fatty acid esters with the structure shown in Formula III.

[0015] Preferably, the kinematic viscosity of the synthetic ester-based transmission fluid composition at 100°C is less than 7 cSt.

[0016] This invention provides a method for preparing the synthetic ester-based transmission fluid composition described above, comprising the following steps: The dispersant, anti-wear and friction reducing agent, antioxidant, corrosion inhibitor and synthetic ester base oil are heated and mixed to obtain the synthetic ester transmission fluid composition.

[0017] The present invention provides the application of the synthetic ester-based transmission fluid composition described in the above technical solution or the synthetic ester-based transmission fluid composition prepared by the preparation method described in the above technical solution as a transmission fluid for electric vehicles.

[0018] This invention provides a synthetic ester-based transmission fluid composition, comprising the following components in weight percentages: 1-3% dispersant, 0.5-1.5% anti-wear and friction-reducing agent, 2-4% antioxidant, 0.05-0.2% corrosion inhibitor, and the balance being synthetic ester base oil; the antioxidant includes liquid octylbutyldiphenylamine and N-phenyl-α-naphthylamine, and the synthetic ester base oil includes one or more of the following: adipate di(fatty alcohol) ester with the structure shown in Formula I, trimethylolpropane fatty acid ester with the structure shown in Formula II, and pentaerythritol fatty acid ester with the structure shown in Formula III. This invention, through the selection and optimal ratio of synthetic ester base oil and functional additives, achieves synergistic optimization of the electrical safety performance, extreme pressure anti-wear performance, thermal oxidation stability, and thermal conductivity of the synthetic ester-based transmission fluid composition, completely solving the technical problems of increased conductivity under strong electric fields, high leakage risk, easy oxidation at high temperatures, and insufficient protective capability in traditional ester-based transmission fluids. Compared with the prior art, this invention has the following beneficial effects: This invention effectively solves the technical challenge of easy ionization and charge imbalance of synthetic ester base oils and polar anti-wear additives under strong electric fields by precisely blending base oil structure and functional additive system, achieving a balance between electrical and lubrication performance. The transmission fluid of this invention can maintain extremely low conductivity and high breakdown voltage for a long time. The extremely low conductivity completely avoids safety hazards such as charge migration and leakage during the operation of high-voltage electric drive systems, while the high breakdown voltage effectively resists extreme voltage impacts, comprehensively ensuring the insulation safety and operational stability of core electrical components such as motors, electronic controls, and reducers. Simultaneously, combined with anti-wear and friction-reducing agents, it can form a stable, high-strength protective oil film on the surface of metal components such as gears and bearings, significantly improving the oil's extreme pressure anti-wear and anti-micro-pitting capabilities, effectively solving the surface fatigue wear problem of transmission components under high-speed and high-load conditions, and significantly extending the service life of electric drive transmission components.

[0019] This invention optimizes the compatibility between antioxidants and synthetic ester base oils, significantly overcoming the technical limitations of traditional ester oils' susceptibility to high-temperature oxidation. Furthermore, this invention achieves a significant improvement in the initial oxidation temperature and high-temperature thermal oxidation stability of the transmission fluid through a precise matching of a liquid octylbutyldiphenylamine and N-phenyl-α-naphthylamine complex antioxidant system with a synthetic ester base oil of a specific structure. The oil is less prone to oxidation and deterioration under long-term high-temperature operation, effectively inhibiting the formation of acidic substances and deposits, and preventing corrosion and blockage damage to motor coils, insulation materials, and precision transmission structures caused by increased acid value and impurity precipitation. This fundamentally improves the safety and stability of the electric drive system during high-temperature operation.

[0020] The synthetic ester-based transmission fluid composition provided by this invention has excellent viscosity parameter adaptability, with a kinematic viscosity of less than 7 cSt at 100°C. Combined with the inherent high thermal conductivity of synthetic ester base oil, it has a rapid and efficient heat dissipation capability, which can promptly remove the frictional heat and working heat generated during the operation of core components such as motors, bearings, and gears. This effectively solves the problem of local overheating caused by the high power density of integrated electric drive systems, reduces the risk of system thermal decay failure, and ensures the continuous and efficient operation of the electric drive system.

[0021] The synthetic ester-based transmission fluid composition provided by this invention exhibits strong stability. Through the compounding of dispersants, corrosion inhibitors, antioxidants, and anti-wear agents, the components synergistically enhance each other, not only avoiding the performance antagonism between polar additives and ester base oils, but also significantly improving the oil's hydrolytic stability, corrosion and rust prevention capabilities, and long-term service stability. The oil aging rate is significantly slowed down, effectively extending the transmission fluid change interval, reducing the operation and maintenance costs of new energy vehicle electric drive systems, and achieving efficient, long-term, and safe lubrication protection for integrated electric drive transmission systems in electric vehicles. It is suitable for the full-condition usage requirements of current high-pressure, high-speed, and highly integrated new energy electric drive systems. Attached Figure Description

[0022] Figure 1 The conductivity curves of the examples and comparative samples as a function of temperature are shown. Detailed Implementation

[0023] This invention provides a synthetic ester-based transmission fluid composition comprising the following components in weight percentages: 1-3% dispersant, 0.5-1.5% anti-wear and friction-reducing agent, 2-4% antioxidant, 0.05-0.2% corrosion inhibitor, and the balance being synthetic ester base oil; wherein the antioxidant comprises liquid octylbutyldiphenylamine and N-phenyl-α-naphthylamine, and the synthetic ester base oil comprises one or more of the following: di(fatty alcohol) adipic acid ester with the structure shown in Formula I, trimethylolpropane fatty acid ester with the structure shown in Formula II, and pentaerythritol fatty acid ester with the structure shown in Formula III; Formula I, Formula II Equation III, where R1, R2, R3, and R4 are independently C4-C 14 Alkyl groups.

[0024] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0025] The synthetic ester-based transmission fluid composition provided by the present invention comprises 1-3% dispersant, preferably 2-2.5%, and in the examples, it can be 2, 2.3, 2.4, 2.5, or 3%. In the present invention, the dispersant preferably comprises one or more of monoalkenyl succinimide, dienyl succinimide, and polyisobutylene succinimide.

[0026] The synthetic ester-based transmission fluid composition provided by this invention comprises 0.5-1.5% (by weight) an anti-wear and friction-reducing agent, which in the examples can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%. In this invention, the anti-wear and friction-reducing agent preferably comprises one or more of ammonium phosphate salt, tricresyl phosphate, octadecyl phosphate, and zinc diisooctyl dithiophosphate. In this invention, the ammonium phosphate salt is purchased from AW319 of Zhongke Runmei Lubricating Materials Technology Co., Ltd.

[0027] The synthetic ester-based transmission fluid composition provided by this invention comprises 2-4% antioxidant by weight percentage, and in the examples, it can be 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, or 4%. In this invention, the antioxidant preferably comprises liquid octylbutyldiphenylamine and N-phenyl-α-naphthylamine. The preferred mass ratio of the liquid octylbutyldiphenylamine to N-phenyl-α-naphthylamine is (2.996-3.002):(2.997-3.004), and in the examples, it can be 2.996:3.002, 2.996:3.004, 3.002:2.997, or 3.000:3.000.

[0028] The synthetic ester-based transmission fluid composition provided by this invention comprises 0.05-0.2% corrosion inhibitor by weight percentage, and in the examples, this can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2%. In this invention, the corrosion inhibitor preferably comprises one or more of a benzotriazole derivative, a thiadiazole derivative, and dodecenylsuccinic acid. Specifically, the benzotriazole derivative can be N,N-di(2-ethylhexyl)-4-methyl-1H-benzotriazole-1-methylamine. Specifically, the thiadiazole derivative can be 2,5-bis(octyldithio)thiadiazole.

[0029] The synthetic ester-based transmission fluid composition provided by the present invention comprises, by weight percentage, the balance being synthetic ester base oil.

[0030] In this invention, the synthetic ester base oil includes one or more of the following: adipate di(fatty alcohol) ester with the structure shown in Formula I, trimethylolpropane fatty acid ester with the structure shown in Formula II, and pentaerythritol fatty acid ester with the structure shown in Formula III. Formula I, Formula II Formula III.

[0031] In this invention, R1 is preferably C4-C. 14 Alkyl groups, more preferably C6-C 10 The alkyl group can specifically be C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, or C 10 Alkyl group. R2 is preferably C4-C. 14 Alkyl groups, more preferably C6-C 10 The alkyl group can specifically be C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, or C 10 Alkyl group. R3 is preferably C4-C. 14 Alkyl groups, more preferably C6-C 10 The alkyl group can specifically be C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, or C 10 Alkyl group. R4 is preferably C4-C. 14 Alkyl groups, more preferably C6-C 10 The alkyl group can specifically be C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, or C 10 alkyl.

[0032] In this invention, the synthetic ester base oil more preferably comprises one or more of di(tetrazolyl) adipate, trimethylolpropane octyl decanoate, and pentaerythritol fatty acid esters with the structure shown in Formula III. Specifically, the pentaerythritol fatty acid ester with the structure shown in Formula III can be an ExxonMobil Esterex NP451 synthetic ester.

[0033] In this invention, the kinematic viscosity of the synthetic ester-based transmission fluid composition at 100°C is preferably below 7 cSt.

[0034] This invention provides a method for preparing the synthetic ester-based transmission fluid composition described above, comprising the following steps: The dispersant, anti-wear and friction reducing agent, antioxidant, corrosion inhibitor, and synthetic ester base oil are heated and mixed to obtain the synthetic ester-based transmission fluid composition. In this invention, the heating and mixing temperature is preferably 70-75°C. The heating and mixing is carried out under stirring. The heating and mixing continues until the above components are completely dissolved and homogeneous.

[0035] The present invention provides the application of the synthetic ester-based transmission fluid composition described in the above technical solution or the synthetic ester-based transmission fluid composition prepared by the preparation method described in the above technical solution as a transmission fluid for electric vehicles.

[0036] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0037] Example 1: Add 7.000g of dispersant (polyisobutylene succinimide), 3.002g of anti-wear and friction reducing agent (octadecyl phosphate), 2.996g of antioxidant (liquid octylbutyldiphenylamine), 3.002g of antioxidant (N-phenyl-α-naphthylamine), 0.300g of corrosion inhibitor (1H-benzotriazol-1-yl-N,N-di(2-ethylhexyl)-4-methylmethylamine), and 283.7g of di(tridecyl) adipate to a beaker, and stir at 70°C until completely dissolved to obtain ester-based electric vehicle transmission fluid composition 1.

[0038] Example 2: Add 7.000g of dispersant (polyisobutylene succinimide), 3.000g of anti-wear and friction reducing agent (octadecyl phosphate), 2.996g of antioxidant (liquid octylbutyldiphenylamine), 3.004g of antioxidant (N-phenyl-α-naphthylamine), 0.3g of corrosion inhibitor (1H-benzotriazol-1-yl-N,N-di(2-ethylhexyl)-4-methylmethylamine), and 283.7g of trimethylolpropane octyl decanoate to a beaker, and stir at 70°C until completely dissolved to obtain ester-based electric vehicle transmission fluid composition 2.

[0039] Example 3: Add 7.000g of dispersant (polyisobutylene succinimide), 3.000g of anti-wear and friction-reducing agent (octadecyl phosphate), 3.002g of antioxidant (liquid octylbutyldiphenylamine), 2.997g of antioxidant (N-phenyl-α-naphthylamine), 0.301g of corrosion inhibitor (1H-benzotriazol-1-yl-N,N-di(2-ethylhexyl)-4-methylmethylamine), and 283.7g of pentaerythritol ester (ExxonMobil Esterex NP451 synthetic ester) to a beaker, and stir at 70°C until completely dissolved to obtain ester-based electric vehicle transmission fluid composition 3.

[0040] Example 4: Add 7.000g of dispersant (diene succinimide), 3.000g of anti-wear and friction reducing agent (tricresol phosphate), 2.996g of antioxidant (liquid octylbutyldiphenylamine), 3.004g of antioxidant (N-phenyl-α-naphthylamine), 0.3g of corrosion inhibitor (1H-benzotriazol-1-yl-N,N-di(2-ethylhexyl)-4-methylmethylamine), and 283.7g of di(tridecyl) adipate to a beaker, and stir at 70°C until completely dissolved to obtain ester-based electric vehicle transmission fluid composition 4.

[0041] Example 5: Add 7.000g of dispersant (diolefin succinimide), 3.000g of anti-wear and friction reducing agent (ammonium phosphate, purchased from Zhongke Runmei Lubricating Materials Technology Co., Ltd. AW319), 3.000g of antioxidant (liquid octylbutyldiphenylamine), 3.000g of antioxidant (N-phenyl-α-naphthylamine), 0.3g of corrosion inhibitor (1H-benzotriazol-1-yl-N,N-di(2-ethylhexyl)-4-methylmethylamine), and 283.7g of di(tridecyl) adipate to a beaker, and stir at 70°C until completely dissolved to obtain ester-based electric vehicle transmission fluid composition 5.

[0042] The comparative sample used in the following test examples is a commercially available electric vehicle transmission fluid (the commercially available ETF was purchased from Idemitsu E Axle Fluid TYPE-A oil-cooled electric drive fluid in Japan), which is compared with the performance of the examples.

[0043] Test example: This test case examines the main performance characteristics of the embodiments and comparative examples, particularly electrical properties, thermal stability, and tribological properties. Electrical properties mainly include conductivity and breakdown voltage. The conductivity test results are shown below. Figure 1Conductivity testing: Following the ASTM D4308 standard for determining the conductivity of liquid hydrocarbons, the conductivity of the samples was measured using an Emcee 1154 precision conductivity meter (manufacturer: Emcee Electronics, USA). This instrument has a measurement range of 0.01-200000.00 pS / m (1 pS / m = 10⁻¹² S / m) and an applicable temperature range of 30-150 ℃. First, the prepared oil was placed in the outer cavity of the measuring tank, and heating was stopped at 150 ℃. The conductivity value at this temperature was recorded. Subsequently, the conductivity data was recorded simultaneously for every 5 ℃ decrease in temperature until the temperature dropped to 30 ℃. Finally, a line graph showing the conductivity-temperature relationship was plotted based on the obtained data. The breakdown voltage performance test results are shown in Table 1. Breakdown voltage performance test: According to GB / T 507 Insulating Oil Breakdown Voltage Test Method, the breakdown voltage of the samples was measured using a ZHNY1701 fully automatic insulating oil breakdown voltage tester (manufacturer: Shandong Zhonghui Instrument Co., Ltd.). The instrument's measurement range is 0.00-80.00 kV. First, the prepared oil was placed in the measuring tank and allowed to stand for 3 minutes. Then, it was stirred, and the voltage was increased at a rate of 2.0 kV / s until the sample broke down. After the sample broke down, the instrument automatically recorded the value and entered a resting cycle (resting before the second breakdown) until 6 tests were completed. After 6 measurements, the instrument automatically calculated the average value.

[0044] Thermal conductivity and thermal stability properties mainly include thermal conductivity and initial oxidation temperature. Thermal conductivity performance testing: According to ASTM D2717 standard, thermal conductivity was tested at room temperature (20-25 ℃) using a thermal conductivity meter (model: TC3000E; manufacturer: Xi'an Xiaxi Electronic Technology Co., Ltd.) and the transient hot wire method. The average of three measurements was taken. Initial oxidation temperature performance testing: According to SH / T0719—2002 "Determination of Oxidation Induction Period of Lubricating Oil (Pressure Differential Scanning Calorimetry)" standard, a high-pressure differential scanning calorimeter (model: DSC204HP; manufacturer: NETZSCH, Germany) was used. The oxygen pressure was 3.5 MPa, the flow rate was 100 mL / min, and the heating rate was 10 K / min.

[0045] In addition, tribological properties and copper strip corrosion performance were tested. The tribological properties of the samples were tested using an SRV-V tester (manufacturer: Optimol Grease GmbH, Germany). The steel ball diameter was 10 mm, and the steel disk diameter was 24 mm with a thickness of 7.9 mm. Both the ball and disk were made of AISI 52100 bearing steel with a hardness of HRC 60±2 and a root mean square surface roughness (RMS) of approximately 20 nm. Test conditions: load 100 N, frequency 25 Hz, temperature 150 ℃, stroke 1 mm, test time 60 min. Copper strip corrosion was tested according to GB / T 5096 method, at 100℃ for 3 hours.

[0046] The performance test results of the samples obtained in Examples 1-5 and the control sample are shown in Table 1.

[0047] Table 1. Test results of main performance of products and comparative samples in Examples 1-5.

[0048] Figure 1 The figures show the conductivity versus temperature curves for Examples 1-3 and the control sample. Figure 1 As can be seen from Table 1, the conductivity of the embodiments and the comparative sample increases with increasing temperature. Compared to the comparative sample, the conductivity of the three embodiments is lower, effectively avoiding leakage risks in high-voltage electrical systems. Table 1 shows that, compared to the comparative sample, Embodiments 1 and 2 have higher breakdown voltages and superior insulation. Table 1 also shows that, compared to the comparative sample, the three embodiments have higher thermal conductivity and higher initial oxidation temperature, exhibiting superior thermal conductivity and thermal stability. The higher flash point of Embodiments 1, 2, and 3 compared to the comparative sample indicates that the synthetic ester-based transmission oil has a greater high-temperature safety advantage. Tribological performance test results show that Embodiments 1 and 2 offer more outstanding wear protection. Simultaneously, the embodiments exhibit better copper strip corrosion resistance, ensuring the oil's compatibility and protection capability for the copper wire windings of the transmission system.

[0049] Comparative Example 1: The difference from Example 1 is that the base oil is PAO4 base oil.

[0050] Comparative Example 2: The difference from Example 1 is that the base oil is short-chain dioctyl adipate.

[0051] Comparative Example 3: The difference from Example 1 is that a single N-phenyl-α-naphthylamine antioxidant was used (the mass of the N-phenyl-α-naphthylamine antioxidant was 5.998 g).

[0052] Comparative Example 4: The difference from Example 1 is that it does not contain anti-wear and friction-reducing agent (the mass of di(tridecyl) adipic acid ester is 286.702 g).

[0053] Comparative Example 5: The difference from Example 1 is that a single liquid octylbutyldiphenylamine antioxidant (the mass of the liquid octylbutyldiphenylamine antioxidant is 5.998 g) was used.

[0054] Comparative Example 6: The difference from Example 1 is the addition of 3% anti-wear and friction-reducing agent (9.000g octadecyl phosphate, and 277.702g of di(tridecyl) adipic acid ester). Table 2. Main performance test results of the products in Example 1 and Comparative Examples 1-6

[0055] In Comparative Example 1, a non-polar PAO was used. Compared with Example 1, it had a lower flash point, poorer thermal conductivity, weaker antioxidant properties, and slightly insufficient anti-wear properties, failing to achieve synergy between ester base oil and polar additives. In Comparative Example 2, the short-chain synthetic ester had lower viscosity and lower breakdown voltage. Comparative Examples 3 and 5 used a single antioxidant, and their initial oxidation temperatures were both lower than those of Example 1, indicating that the synergistic effect of the antioxidant compound plays an important role in improving oxidation life. In Comparative Example 4, no anti-wear and friction-reducing agent was used, resulting in poor tribological properties that could not meet the friction performance protection requirements of electric vehicle transmission fluid. In Comparative Example 6, an excessive amount of anti-wear and friction-reducing agent led to a decrease in breakdown voltage.

[0056] As can be seen from the above embodiments, the present invention provides a novel ester-based electric vehicle transmission fluid composition. This composition has a kinematic viscosity of less than 7 cSt at 100°C, exhibits extremely low electrical conductivity, high breakdown voltage, and excellent thermal conductivity, while also demonstrating a high initial oxidation temperature and excellent oxidation resistance. The extremely low electrical conductivity effectively avoids the risk of leakage in high-voltage electrical systems, while the high breakdown voltage ensures the insulation safety of the motor and electronic control components under extreme operating conditions. The excellent thermal conductivity can quickly dissipate the heat generated by components such as motors, bearings, and gears, preventing localized overheating. The high initial oxidation temperature combined with excellent oxidation resistance significantly slows down the oil aging process and extends the oil change interval, thereby providing long-lasting, efficient, and reliable lubrication protection for the electric vehicle transmission system.

[0057] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A synthetic ester-based transmission fluid composition, characterized in that, The product comprises the following components in weight percentage: 1-3% dispersant, 0.5-1.5% anti-wear and friction reducing agent, 2-4% antioxidant, 0.05-0.2% corrosion inhibitor, and the balance being synthetic ester base oil; wherein the antioxidant includes liquid octylbutyldiphenylamine and N-phenyl-α-naphthylamine, and the synthetic ester base oil includes one or more of the following: di(fatty alcohol) adipic acid ester with the structure shown in Formula I, trimethylolpropane fatty acid ester with the structure shown in Formula II, and pentaerythritol fatty acid ester with the structure shown in Formula III; Formula I, Formula II Equation III, where R1, R2, R3, and R4 are independently C4-C 14 Alkyl groups.

2. The synthetic ester-based transmission fluid composition according to claim 1, characterized in that, The dispersant includes one or more of monoalkenyl succinimide, dienyl succinimide, and polyisobutylene succinimide.

3. The synthetic ester-based transmission fluid composition according to claim 1, characterized in that, The anti-wear and friction-reducing agent includes one or more of ammonium phosphate salt, tricresyl phosphate, octadecyl phosphate, and zinc diisooctyl dithiophosphate.

4. The synthetic ester-based transmission fluid composition according to claim 1, characterized in that, The corrosion inhibitors include one or more of benzotriazole derivatives, thiadiazole derivatives, and dodecenylsuccinic acid.

5. The synthetic ester-based transmission fluid composition according to claim 4, characterized in that, The corrosion inhibitor includes one or more of 1H-benzotriazol-1-yl-N,N-di(2-ethylhexyl)-4-methylmethylamine, 2,5-bis(octyldithio)thiadiazole, and dodecenylsuccinic acid.

6. The synthetic ester-based transmission fluid composition according to claim 1, characterized in that, R1, R2, R3, and R4 are independently C6-C 10 Alkyl groups.

7. The synthetic ester-based transmission fluid composition according to claim 1, characterized in that, The synthetic ester base oil includes one or more of di(tetrazolyl) adipate, trimethylolpropane octyl decanoate, and pentaerythritol fatty acid esters with the structure shown in Formula III.

8. The synthetic ester-based transmission fluid composition according to any one of claims 1 to 7, characterized in that, The synthetic ester-based transmission fluid composition has a kinematic viscosity of less than 7 cSt at 100°C.

9. A method for preparing the synthetic ester-based transmission fluid composition according to any one of claims 1 to 8, characterized in that, Includes the following steps: The dispersant, anti-wear and friction reducing agent, antioxidant, corrosion inhibitor and synthetic ester base oil are heated and mixed to obtain the synthetic ester transmission fluid composition.

10. The synthetic ester-based transmission fluid composition according to any one of claims 1 to 8 or the synthetic ester-based transmission fluid composition prepared by the preparation method according to claim 9, as a transmission fluid for electric vehicles.

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