A substantially zinc-free hydraulic fluid is provided. The substantially zinc-free hydraulic fluid contains a calcium detergent, an ashless antioxidant, and a metal-free phosphorous containing anti-wear agent. In one embodiment, the fluid contains at least 90 weight percent of a base oil having less than 500 ppm sulfur, a calcium detergent in an amount to deliver 5 ppm to 200 ppm calcium to the fluid, at least one metal-free phosphorus containing anti-wear agent to provide 10 ppm to 150 ppm phosphorous, and one or more ashless antioxidants. A method of lubricating a hydraulic system with the substantially zinc-free fluid is also provided.

A composition comprising water and a polyalkylene glycol having an allyl content of less than 20 eq/g, which composition has reduced foaming properties and preferably a biodegradability of at least 60% as determined using OECD 301F. The polyalkylene glycol can be made by forming a first intermediate comprising an oxypropylene block by reacting propylene oxide with a polyol initiator in the presence of a Double Metal Cyanide catalyst, and then reacting the first intermediate with ethylene oxide in the presence of a KOH catalyst.

An object is to provide a lubricant oil composition excellent in biodegradability, lubricating property (extreme pressure property), stability against oxidation and demulsibility, having low toxicity and bioaccumulation property in an aquatic life, and excellent in stability against shearing even in the presence of water.

A lubricant oil composition comprises 100 mass parts of the following ester compound (A), 0.1 to 1.5 mass parts of the following amine salt (B) of an acidic phosphoric acid ester, 0.3 to 2.0 mass parts of an amine-based oxidation preventing agent (C), and 0.3 to 2.0 mass parts of a phenol-based oxidation preventing agent (D), (A) the ester compound comprising a molar percentage of 20 to 30 mol % of a constituent component (a) derived from pentaerythritol, a molar percentage of 55 to 79 mol % of a constituent component (b) derived from a straight-chain fatty acid having a carbon number of 14 to 22, and a molar percentage of 1 to 15 mol % of a constituent component (c) derived from adipic acid, wherein a ratio [(c) mol %/(b) mol %] of the molar percentage of the constituent component (b) with respect to the molar percentage of the constituent component (c) is 0.02 to 0.25 and wherein the ester compound has a hydroxyl value of 10 to 100 mgKOH/g, (B) the amine salt of an acidic phosphoric acid ester represented by the following formula (1),

##STR00001## (in the formula (1), n represents an integer of 1 or 2, R represents a straight-chain alkyl group having a carbon number of 4 to 6, and R represents hydrogen or an alkyl group having a carbon number of 11 to 14.).

A lubricant composition comprising an oil-soluble polyalkylene glycol; an ester compound selected from the group of natural esters and synthetic esters, and combinations thereof; and an additive mixture comprising an antioxidant and an anticorrosive, wherein the anticorrosive is selected from neutral alkali metal and alkaline earth metal salts of sulfonic acids, carboxylic acids, naphthoic acids, naphthenic acids, benzoic acids and phosphoric acids, and derivatives and combinations thereof.

A shock absorber that includes a pressure tube that defines a working chamber having a hydraulic fluid located therein; a piston assembly positioned in the working chamber, and dividing the working chamber into an upper working chamber and a lower working chamber; and a piston rod engaged with the piston assembly that moves the piston assembly in the working chamber, wherein the hydraulic fluid includes a primary oil, a secondary oil, and an additive package, the secondary oil includes at least a gas-to-liquid oil in an amount that ranges between 4.0 wt % to 10.0 wt % relative to a total amount of the hydraulic fluid, and the hydraulic fluid includes a flash point of at least 174 degrees C.

The present invention provides a magnetic viscous fluid comprising a magnetic particle, at least one selected from ester base synthetic oil, ether base synthetic oil, and alkylnaphthalene having an alkyl group with 10 to 20 carbons, an inorganic cation exchanger with a siloxane bond, and silicone oil.

Provided are a shock absorber-lubricating oil composition, a lubricating oil additive, and a method for adjusting the friction characteristics of the shock absorber-lubricating oil composition, capable of making both operation stability and ride comfort compatible with each other. A shock absorber-lubricating oil composition contains a base oil and a friction modifier. The friction modifier contains a pentaerythritol ester. The base oil contains an ester oil as a main component.

The present invention provides a magnetic viscous fluid comprising a magnetic particle, base oil, an inorganic cation exchanger with a siloxane bond, and silicone oil. A difference AB between a solubility parameter A of the base oil and a solubility parameter B of the silicone oil is 1.3 (cal/cm.sup.3).sup.1/2 or more.

Disclosed are solvency enhancer compositions, for example, as additives to lubricating oils and as formulated in lubricating oil compositions and associated methods of preparation and use thereof. The compositions and methods can dissolve at least one of oxidation products and other organic polar compounds, due to lubricant degradation, formed and suspended in oil compositions including adding an effective amount of a solvency enhancer to the oils, wherein the solvency enhancer includes Guerbet alcohols. Further described are methods for dissolving organic deposits in an oil system including adding an effective amount of a solvency enhancer to the oil system, wherein the solvency enhancer includes Guerbet alcohols. Also provided are methods for preventing sludge and varnish formation in in-service oils including adding an effective amount of a solvency enhancer to the oils, wherein the solvency enhancer includes Guerbet alcohols.

A composition has a high content of saturated or unsaturated isoparaffinic hydrocarbons having 12-24 carbon atoms and a polyalkyl (meth)acrylate. A method prepares such composition and the composition can be used to raise the flash point of hydraulic fluids where a good low temperature flow is important, e.g. compressor oils, shock absorber fluids, power steering fluids and, central hydraulic fluids.