1. Field of the Invention
This invention relates to a composition suitable for use in mechanical power transmission units. More particularly, the invention relates to compositions specifically adapted for use with traction drives and to a process for operating traction drives.
2. Prior Art
Heretofore, gears and hydraulic devices have been used for power transmission or speed control. A system of drives, called traction drives (rolling friction drive devices), which resort to point contact or line contact between rolling solid bodies has found recognition. These traction drives are particularly useful in industrial machines because they provide high power transmission efficiency without the vibration characteristic of devices using gears and like positive forms of engagement.
As the fluid to be interposed between contact parts of such traction drives, there must be selected a lubricant which proves most suitable from the functional point of view. Specifically, the fluid intervening between contact parts is required to possess an ability to undergo reversible glass transition, viscosity increasing, and enhance the efficiency of power transmission between surfaces of rolling contact under high pressure and, on departure from such contact surfaces, immediately return to its original fluid state. It must also be capable of precluding direct contact between metal bodies, preventing metal bodies from seizure, wear and fatigue damage and, similarly to lubricants of all kinds fulfilling important functions of preventing occurrence of rust and elevation of temperature.
Friction or traction drive devices for transmission of mechanical power have been disclosed in a number of reports in prior technical literature. They are dealt with in full detail in U.S. Pat. Nos. 3,394,603 and 3,411,369; the Journal of Chemical and Engineering Data, Vol. 5, No. 4, p.p. 499-507 (1960), and Hewko et al., in Proceedings of the Symposium on Rolling Contact Phenomena, p.p. 157-185 (1962), Elsevier, Amsterdam, Netherlands, for example.
As compositions for use in traction drives, a host of substances have been advanced, including mineral oils (Japanese Patent Publication No. 24,635/1964), mixtures of dialkyl aromatic hydrocarbons with diarylalkanes (Japanese Patent Publication 40,525/1972), polymethylmethacrylate (Japanese Pat. Publication No. 31,828/1973), adamantanes (Japanese Pat. Publications 42,067/1973 and 42,068/1973), polyolefins (Japanese Patents KOKAI 4,766/1971 and 2,229/1972) and alkylnaphthalenes (U.S. Pat. No. 2,549,377), for example. Japanese Patent KOKAI 40,726/1980 has proposed fluids which are obtained by hydrogenating bis-(.alpha.-methylbenzyltoluene) and/or bis-(.alpha.-methylbenzyl)-xylene.
Besides, proposals abound which concern naphthenic oils having naphthenic rings. These naphthenic oils include dicyclohexylethane (U.S. Pat. No. 3,577,361), dicyclohexylpropane (Japanese Patent Publication 36,105/1978), hydrogenated condensation ring compounds (U.S. Pat. No. 3,411,369), naphthenes containing at least one saturated carbon-containing cyclic ring (U.S. Patent 3,440,894), naphthenes containing at least two saturated carbon-containing cyclic rings (U.S. Pat. Nos. 3,925,217), and mixtures of naphthenes and paraffins (U.S. Pat. Nos. 3,595,796 and 3,595,797), and an oil which is obtained by hydrogenating the product of alkylation of xylene and/or toluene with styrene (Japanese Patent KOKAI No. 43,108/1980), for example.
U.S. Pat. Nos. 3,440,894 and 3,925,217 mentioned above embrace a wide range of naphthenic compounds and cite a large number of naphthenes by way of example. Most of them are compounds which possess one or two hydrogenated rings. Among the compounds disclosed therein, those which possess three or more hydrogenated rings are limited to a small number, including tercyclohexyls 1,2,3-tricyclohexylpropane and tricyclohexylmethane, for example. Although they have a high traction factor, they have poor practical use because of high viscosity or high crystal-precipitating temperature. It is noted from the prior technical literature that naphthenic oils containing hydrogenated rings are possessed of generally outstanding properties for lubricants, particularly those to be used in traction drives.