Lubricating oil composition

Abstract: A lubricating oil composition having improved fuel economy, wear resistance and antioxidancy properties which comprise a lubricating oil basestock, an oil-soluble copper salt, an oil-soluble molybdenum salt, a Group II metal salicylate and a borated polyalkenyl succinimide.

Description: This invention relates to a lubricating oil composition for internal combustion engines having improved fuel economy, wear resistance and antioxidancy properties. While the majority of moving parts in an internal combustion engine are in a state of hydrodynamic lubrication, some sliding parts such as pistons and valve trains are in a boundary lubrication state. In order to provide wear resistance caused by friction in the boundary lubrication state, it is necessary to provide the engine oil with additives to reduce wear. For many years, zinc dialkyldithiophosphates ("ZDDP") have been a standard antiwear additive. While ZDDP is a good antiwear agent, it has negative impacts on fuel economy. Thus it is usually necessary to include a friction modifier for fuel economy purposes. Both antiwear and friction modifiers function through adsorption on the sliding metal surface and may interfere with each other's respective functions. U.S. Patent 4,705,641 describes an engine oil having improved antiwear and antioxidancy properties. The engine oil contains from 0.002 to 0.3 wt% of a copper salt and from 0.004 to 0.3 wt% of a molybdenum salt. This combination is also stated to reduce the treat rate of ZDDP necessary for wear protection. It would be desirable to improve the friction modifying properties of molybdenum salt to meet the increasing fuel economy demands placed on modern engine oils due to environmental considerations. This invention relates to a lubricating oil composition having improved fuel economy, wear resistance and antioxidancy which comprises: (a) a lubricating oil basestock; (b) from 0.002 to 1.0 wt%, based on oil composition, of a copper salt; (c) from 0.004 to 4 wt%, based on oil composition, of a molybdenum salt; (d) from 50 to 4000 ppmw, based on oil composition, of metal atoms present as metal salicylate wherein the metal is selected from Group II metals; and (e) at least 2 wt%, based on oil composition, of a borated polyalkenyl succinimide. In another embodiment, this invention relates to a method for improving fuel economy, wear resistance and antioxidancy properties in an internal combustion engine which comprises operating the engine with the lubricating oil composition described above. The engine oil according to the invention requires a major amount of lubricating oil basestock. The lubricating oil basestock can be derived from natural lubricating oils, synthetic lubricating oils, or mixtures thereof. Suitable lubricating oil basestocks include basestocks obtained by isomerization of synthetic wax and slack wax, as well as hydrocrackate basestocks produced by hydrocracking (rather than solvent extracting) the aromatic and polar components of the crude. In general, the lubricating oil basestock will have a kinematic viscosity ranging from about 2 to about 1,000 cSt at 40°C. Natural lubricating oils include animal oils, vegetable oils (e.g., castor oils and lard oil), petroleum oils, mineral oils, and oils derived from coal or shale. Synthetic oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins, alkylbenzenes, polyphenyls, alkylated diphenyl ethers, alkylated diphenyl sulfides, as well as their derivatives, analogs, and homologs thereof, and the like. Synthetic lubricating oils also include alkylene oxide polymers, interpolymers, copolymers and derivatives thereof wherein the terminal hydroxyl groups have been modified by esterification, etherification, etc. Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids with a variety of alcohols. Esters useful as synthetic oils also include those made from C 5 to C 12 monocarboxylic acids and polyols and polyol ethers. Silicon-based oils (such as the polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils) comprise another useful class of synthetic lubricating oils. Other synthetic lubricating oils include liquid esters of phosphorus-containing acids, polymeric tetrahydrofurans, polyalphaolefins, and the like. The lubricating oil may be derived from unrefined, refined, re-refined oils, or mixtures thereof. Unrefined oils are obtained directly from a natural source or synthetic source (e.g., coal, shale, or tar sands bitumen) without further purification or treatment. Examples of unrefined oils include a shale oil obtained directly from a retorting operation, a petroleum oil obtained directly from distillation, or an ester oil obtained directly from an esterification process, each of which is then used without further treatment. Refined oils are similar to the unrefined oils except that refined oils have been treated in one or more purification steps to improve one or more properties. Suitable purification techniques include distillation, hydrotreating, dewaxing, solvent extraction, acid or base extraction, filtration, and percolation, all of which are known to those skilled in the art. Rerefined oils are obtained by treating refined oils in processes similar to those used to obtain the refined oils. These rerefined oils are also known as reclaimed or reprocessed oils and often are additionally processed by techniques for removal of spent additives and oil breakdown products. Copper salts are oil-soluble and may be cuprous or cupric salts. Copper salts are salts of synthetic or natural organic acids, preferably mono- and dicarboxylic acids. Preferred carboxylic acids are C 10 to C 30 saturated and unsaturated fatty acids and polyisobutenyl succinic acids and their anhydrides wherein the polyisobutenyl group has a number average molecular weight of 700 to 2500. Examples of preferred copper salts include copper oleate, copper stearate, copper naphthenate and the copper salt of polyisobutenyl succinic acid or anhydride wherein the polyisobutenyl group has an average molecular weight 800-1200. The amount of copper salt is preferably from 0.05 to 0.6 wt%, based on lubricating oil composition. Molybdenum salts are oil-soluble salts of synthetic or natural organic acids, preferably salts of mono- and dicarboxylic acids. Preferred carboxylic acids are C 4 to C 30 saturated and unsaturated fatty acids. Examples of preferred molybdenum salts include molybdenum naphthenate, hexanoate, oleate, xanthate and tallate. The amount of molybdenum salt is preferably from .01 to 3.0 wt%, based on lubricating oil composition. The Group II metals in the metal salicylates include beryllium, magnesium, calcium, strontium, and barium. Preferred Group II metal salicylates are magnesium salicylate and calcium salicylate. The amount of Group II metal salicylate is preferably present at from 0.1 to 8 wt%, based on lubricant oil composition provided that the amount of Group II metal atoms present as metal salicylate is from 50 to 4000 ppmw. Borated polyalkenyl succinimide dispersants are described in U.S. Patent 4,863,624. Preferred borated dispersants are boron derivatives derived from polyisobutylene substituted with succinic anhydride groups and reacted with polyethylene amines, polyoxyethylene amines, and polyol amines (PIBSA/ PAM) and are preferably added in an amount from 2 to 16 wt%, based on oil composition. These reaction products are amides, imides or mixtures thereof. The borated dispersants are preferably "over-borated", i.e., they contain boron in an amount from 0.5 to 5.0 wt% based on dispersants. These over-borated dispersants are available from Exxon Chemical Company. The amount of boron in the engine oil should be at least about 500 ppmw, preferably about 900 ppmw. In addition to borated dispersants, other sources of boron which may contribute to the total boron concentration include borated dispersant VI improvers and borated detergents. If desired, the lubricating oil composition may contain other additives known in the art. Such additives include other dispersants, other antiwear agents, other antioxidants, rust inhibitors, corrosion inhibitors, other detergents, pour point depressants, extreme pressure agents, viscosity index improvers, other friction modifiers, antifoam agents and hydrolytic stabilizers. Such additives are described in "Lubricants and Related Products" by Dieter Klamann, Verlag Chemie, Weinheim, Germany, 1984. The lubricating oil compositions can be used in the lubricating system of essentially any internal combustion engine such as automobile and truck engines, marine engines and railroad engines. The invention may be further understood by reference to the following examples. EXAMPLES 1-8 These examples, including comparative examples, demonstrate the effects of the additive combination according to the invention. The ball-on-cylinder (BOC) friction test, 4-ball wear test and differential scanning calometry tests are described as follows. BOC tests were performed using the experimental procedure described by S. Jahanmir and M. Beltzer in ASLE Transactions, 29, No. 3, p. 425 (1985) except that a force of 0.8 Newtons (1 Kg) rather than 4.9 Newtons was applied to a 12.5 mm steel ball in contact with a rotating steel cylinder having a 43.9 mm diameter. The cylinder rotates inside a cup containing a sufficient quantity of lubricating oil to cover 2 mm of the bottom of the cylinder. The cylinder was rotated at 0.25 rpm. The frictional force was continuously monitored by means of a load transducer. In the tests conducted, friction coefficients attained steady state values after 7 to 10 turns of the cylinder. Friction experiments were run at an oil temperature at 104°C. The Four Ball test used is described in detail in ASTM method D-2266. In this test, three balls are fixed in a lubricating cup and an upper rotating ball is pressed against the lower three balls. The test balls utilized were made of AISI 52100 steel with a hardness of 65 Rockwell C (840 Vickers) and a centerline roughness of 25 nm. Prior to the tests, the test cup, steel balls, and all holders were washed with 1,1,1 trichloroethane. The steel balls subsequently were washed with a laboratory detergent to remove any solvent residue, rinsed with water, and dried under nitogen. The Four Ball wear tests were performed at 100°C, 60 kg load, and 1200 rpm for 45 minutes duration. After each test, the balls were washed and the wear scar diameter on the lower balls measured using an optical microscope. Oxidative differential scanning calorimetry (oxidative DSC) is a procedure that assesses the antioxidancy of a lubricating oil. In this DSC test, a sample of oil is heated in air at a programmed rate, e.g., 5°C/minute and the sample temperature rise relative to an inert reference measured. The temperature at which an exothermic reaction occurs (the oxidation onset temperature) is a measure of the oxidative stability of the sample. The oil used in the following examples is a fully formulated 5W-30 oil, to which the components specified in Table 1 have been added. All components are commercially available as noted in the Table. Examples 1 and 2 demonstrate that the combination of copper salt, molybdenum salt, Group II metal salicylate and borated PIBSA-PAM produces superior results in the combination of BOC friction coefficient, 4-ball wear scar and DSC temperature. Comparative examples 3 and 4 show that switching detergent from Mg sulfonate to Mg salicylate has very little effect on the friction coefficient and a negative effect on wear scar diameter and oxidation. Comparative examples 3 and 5 are directed to the effect of non-borated vs. borated PIBSA-PAM dispersant. While the borated PIBSA-PAM shows a significantly reduced friction coefficient and better oxidative stability, there was almost negligible improvement in wear. Changing both the detergent and dispersant, comparative examples 3 and 6, shows improved friction coefficient and oxidation, but little effect on wear scar diameter. In comparing Examples 1 and 2 according to the invention with comparative examples 7 and 8, it can be seen that the combination of Group II metal salicylate and borated PIBSA-PAM provides surprising improvement in friction coefficient, 4-ball wear scar diameter and DSC temperature. EXAMPLES 9-12 These examples concern fuel economy performance as measured by the Sequence VI Screener Test. The ASTM Sequence VI test procedure (SAE JI 423 May 1988) is used for evaluating engine oils and for identifying energy conserving engine oils for passenger cars, vans, and light duty trucks. The recommended practice involves a classification for engine oils that have energy-conserving characteristics under certain operating conditions and are categorized as "Energy Conserving" (tier I) or "Energy Conserving II" (tier II). In accordance with the definitions set forth in the Sequence VI test procedure, Energy Conserving (tier I) and Energy Conserving II (tier II) engine oils are lubricants that demonstrate reduced fuel consumption when compared to specified ASTM reference oils using a procedure which is described in ASTM Research Report No. RR:PD02:1204, "Fuel Efficient Engine Oil Dynamometer Test Development Activities, Final Report, Part II, Aug. 1985." The Sequence VI procedure compares fuel consumption with a candidate oil to that with the ASTM HR (High Reference) SAE 20W-30 Newtonian oil in terms of Equivalent Fuel Economy Improvement (EFEI) by use of the following equation: EFEI = [0.65 (Stage 150) + 0.35 (Stage 275) - 0.61] 1.38 The equation is used to transfer the data obtained in two stages of an older procedure, known as the five-car procedure (published as D-2 Proposal P101 in Volume 05.03 of the 1986 ASTM Book of Standards), which is an alternative method only for use in evaluating engine oils that meet the Energy Conserving (tier I) category. To fulfill the Tier I energy-conserving requirement using the five-car procedure, the candidate oil must meet the performance limits of the classification published as a proposal in Volume 05.03 of the ASTM Book of Standards (D-2 Proposal P102). The five-car average fuel consumption with the candidate oil must be less than that with reference oil HR by at least 1 % and the minimum lower 95% confidence level (LCL95) must be at least 0.3%. When using reference oil HR-2, the average fuel consumption with the candidate oil must be at least 1.5% less than that with reference oil with a minimum LCL95. When the Sequence VI test is used, the results obtained in two of the stages of the test are transformed to an equivalent five-car percent improveent by use of the above equation. The Equivalent Fuel Economy improvement (EFEI) from the Sequence VI test must meet the limits of the aforementioned classification D-2 Proposal P102, with the exception of the LCL95 requirement which applies to only the five-car procedure. For a candidate oil to be categorized as Energy Conserving II the Equivalent Fuel Economy Improvement (EFEI) as described above and must be a minimum of 2.7% when compared to HR-2. Thus Engine oils categorized as "Energy Conserving (tier I) are formulated to improve the fuel economy of passenger cars, vans and light-duty trucks by an EFEI of 1.5% or greater over a standard reference oil in a standard test procedure, whereas oils categorized as "Energy Conserving II" (tier II) are formulated to improve the fuel economy of passenger cars, and vans and light-duty trucks by an EFEI of 2.7% or greater over a standard reference oil in a standard test procedures. Variability problems with batches 6 and 7 of HR oil led to a revised equation by the industry for calculating EFEI in 1991 [2]. This is called "Method 2" and is given by the following equation: where: Cand. δ150:150 is the % difference in BSFC between the HR oil and the candidate oil, both measured at 65.5°C (150°F). Cand. δ275:150 is the % difference in BSFC between the HR oil measured at 65.5°C (150°F) and the candidate oil measured at 135°C (275°F). FM δ275:150 is the % difference in BSFC between the HR oil measured at 150°F and the FM oil measured at 275°F. The date reported in Table 2 are based on fuel economy calculations according to Method 2. The Sequence VI Screener Test is the same as the ASTM Sequence VI Test except that Run stage for the candidate oil is reduced from 31.5 hours at 107°C with BSFC measured every two hours and six replicate BSFC measurements at 5 minute intervals at the end to duplicate Run Stages of two hours at 135°C and six replicate BSFC measurements at five minute intervals at the end. Good correlation between the sequence VI screened test and the ASTM sequence VI test has been established. All formulations contain the same engine oil components and differ only in the detergent. The oils are SAE 5W-20 oils blended to the same TBN and similar kinematic viscosity at 100°C and CCS viscosity at -25°C. Example 9 contains Mg sulfonate detergent and is compared with Example 10 which contains Mg salicylate detergent. Similarly, Example 11 contains Ca sulfonate detergent and is compared with Example 12 which contains Ca salicylate detergent. The results are shown in Table 2. The comparisons of Examples 9 and 11 vs. 10 and 12 show that Group II metal salicylates give improved fuel economy over the metal sulfonates.

Claims: A lubricating oil composition having improved fuel economy, wear resistance and antioxidancy properties which comprises: (a) a lubricating oil base stock; (b) from 0.002 to 1.0 wt%, based on oil composition, of a copper salt; (c) from 0.004 to 4 wt%, based on oil composition, of a molybdenum salt; (d) from 50 to 4000 ppmw, based on oil composition, of metal atoms present as metal salicylate wherein the metal is selected from Group II metals; and (e) at least 2 wt%, based on oil composition, of a borated polyalkenyl succinimide. The composition of claim 1 wherein the copper salt is selected from salts of organic acids. The composition of claim 2 wherein the organic acids are mono- or dicarboxylic acids. The composition of any preceding claim wherein the molybdenum salt is selected from oil-soluble salts of organic acids. The composition of claim 4 wherein the organic acids are C 4 -C 30 saturated or unsaturated carboxylic acids. The composition of any preceding claim wherein the metal salicylate is magnesium salicylate, calcium salicylate or mixtures thereof. The composition of any preceding claim wherein the succinimide is a borated polyisobutenyl succinimide. The composition of any preceding claim wherein the amount of borated succinimide is from 2 to 16 wt%, based on oil composition. The composition of any preceding claim wherein the amount of boron in the oil is at least 500 ppmw, based on oil. A method for improving the fuel economy performance of an internal combustion engine which comprises operating the engine with the engine oil of any preceding claim .

Inventors: VRAHOPOULOU ELISAVET P, VRAHOPOULOU, ELISAVET P.
Applicants: EXXONMOBIL RES & ENG CO, EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
Application year: 1995
Main classification: C10M141
IPC codes: C10N10, C10M163, C10M141, C10N30