The invention provides a grease composition for a speed reducer part of an on-vehicle electric component, the grease composition containing a base oil and a thickener, wherein the base oil is poly-α-olefin or a mixed oil of poly-α-olefin and mineral oil having a kinematic viscosity of 4 to 19 mm.sup.2/s at 100° C. and a pour point of −30° C. or lower, the thickener is a mixture of a diurea compound expressed by formula (1) and a diurea compound expressed by formula (2)

R.sub.1—NHCONH—R.sub.2—NHCONH—R.sub.1  (1)

R.sub.3—NHCONH—R.sub.2—NHCONH—R.sub.3  (2)

wherein R.sub.1 is a straight-chain alkyl group having 8 or 18 carbon atoms, R.sub.2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, and R.sub.3 is an aryl group having 6 to 7 carbon atoms, and a penetration of the grease composition is 220 to 280.

A lubricating oil composition containing a base oil (A), a comb-shaped polymer (B), and an olefin-based copolymer (C), wherein a content of the component (B) is more than 0.80 mass % based on the total amount of the lubricating oil composition, a weight average molecular weight of the component (C) is 500,000 or more, and the lubricating oil composition has a viscosity index of 200 or more and a kinematic viscosity at 100° C. of 9.3 to 11.0 mm.sup.2/s.

A lubricating oil composition for agricultural machines, containing: at least one base oil selected from the group consisting of mineral oil-based base oils and synthetic oil-based base oils; and a polyalkyl methacrylate-based viscosity index improver having a weight average molecular weight of from 20,000 to 80,000, in which a kinematic viscosity at 100° C. is from 8.00 mm.sup.2/s to 10.00 mm.sup.2/s, a kinematic viscosity reduction rate at 100° C. in an ultrasonic shear stability test is 10.0% or less, and a Brookfield viscosity at −40° C. is 20,000 mPa.Math.s or less.

The present disclosure relates to methods of improving viscosity shear stability of a lubricating oil and lubricating oil composition comprising: a base oil of lubricating viscosity; an amount of one or more zinc dialkyl dithiophosphate compound(s);
wherein the lubricating oil composition has one or both of the following ratios: a) a ratio of KV40° C..sub.fresh to a weight % of zinc contributed by the one or more zinc dialkyl dithiophosphate compound(s) based on a total weight of the lubricating oil composition, of greater than 510, wherein KV40° C..sub.fresh is the kinematic viscosity of the fresh lubricating oil composition at 40° C.; and b) a ratio of KV40° C..sub.fresh to a weight % of phosphorus contributed by the one or more zinc dialkyl dithiophosphate compound(s) based on a total weight of the lubricating oil composition, of greater than 560, wherein KV40° C..sub.fresh is the kinematic viscosity of the fresh lubricating oil composition at 40° C.

A lubricating oil composition for an internal combustion engine including: (A) a lubricant base oil having a kinematic viscosity at 100° C. of 2 to 5 mm.sup.2/s; (B) a metallic detergent in an amount of 500 to 2500 mass ppm in terms of Ca and 100 to 1000 mass ppm in terms of Mg, on the basis of the total mass of the composition, the metallic detergent including both (B1) a Ca-containing metallic detergent and (B2) a Mg-containing metallic detergent; (C) a boron-containing additive in an amount of 50 to 1000 mass ppm in terms of boron on the basis of the total mass of the composition, wherein the boron-containing additive is oil-soluble or oil-dispersible and is stable in oil, and wherein the boron-containing additive may compose at least a part of the component (B); and (D) an oil-soluble organic Mo compound in an amount of 100 to 2000 mass ppm in terms of Mo on the basis of the total mass of the composition, wherein a mass ratio (MB/Mg) of boron content of the composition (MB) to Mg content of the composition (Mg) is 0.5 to 10.

A lubricating composition comprises an oil-soluble poly(2-oxazoline) additive having the repeat unit:

—N(COR.sup.1)CH.sub.2CH.sub.2— where the number of repeat units (n) is an integer between 4 and 1000; where the polymer carries an inorganic or organic nucleophilic polymerization terminating group t, and a linear, branched or cyclic hydrocarbyl polymerization initiator group (i); and where R.sup.1 comprises a single or a mixture of linear branched or cyclic hydrocarbyl groups having 1-100 carbon atoms, some or all having 12-100 carbon atoms, or of at least one macro-monomeric hydrocarbyl group with more than 50 carbon atoms provided that when the polymer is a homopolymer and R.sup.1 lacks any hetero atoms; (A) i has a molecular weight of less than 250 g/mol, and R.sup.1 has an average number of carbon atoms of 12 to 50; or (B) n is greater than 15.

The polymer may provide the composition, in the form of a lubricant, with friction modifier, and with low impact on lubricant viscosity.

The polymer may be a homopolymer, a block copolymer or a star polymer.

Provided is an engine oil lubricant composition with improved fuel economy. The engine oil lubricant composition may include about 40 wt % to about 80 wt % of a first oil base stock consisting of a Group IV base oil and about 10 wt % to about 40 wt % of a second oil base stock that is not a Group IV base oil, where these weight percents are based on the total weight of the engine oil lubricant composition. The engine oil lubricant composition can have an HTHS (ASTM D4683) of less than or equal to 2.2 cP at 150° C., a Noack volatility (ASTM D5800) of 25% or less, and an evaporation rate of 6% or less as measured by distillation method DIN 51454 mod. C17-C19.

A lubricating oil composition for internal combustion engines of passenger and commercial four-wheeled vehicles is provided which can exhibit excellent fuel efficiency performance and wear resistance reliability. The lubricating oil composition includes a base oil and a complex polyester mixture. The base oil includes at least one of poly-α-olefin, an ester-based base oil, or a partially hydrogenated mineral oil. The complex polyester mixture includes a polyester obtained by condensing a polyhydric alcohol, a polycarboxylic acid, and a monohydric alcohol having an oxyalkylene group. The content of the complex polyester mixture is 0.01% by mass or more with respect to the total mass of the lubricating oil composition, the high-temperature shear viscosity (HTHS viscosity) at 150° C. is 1.0 mPa.Math.s to 2.6 mPa.Math.s, and the NOACK evaporation amount is 40% or less.

A novel process can be used for the preparation of polyalkyl (meth)acrylate polymers with improved compositional distribution, which leads to better producibility, solubility, and improved performance of the polymers in lubricant compositions, especially in engine oil formulations.

A lubricating oil composition prepared by blending a base oil (A) containing a compound (A1) that is an ester or ether and has two or more aromatic rings, with a polyalkylene glycol (B) is provided. The lubricating oil composition has a high density (i.e., a high bulk modulus), a high viscosity index, and excellent shear stability.