Compositions – Liquid crystal compositions
Patent
1989-10-26
1992-11-03
Stoll, Robert L.
Compositions
Liquid crystal compositions
428 1, 359 62, C09K 1952, C09K 1900
Patent
active
051604515
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a mechanical component consisting of solid bodies or parts of bodies, which are mobile relative to one another and are separated from one another by a fluid organic mass, wherein it is possible to vary the frictional forces acting between the bodies by changing the molecular order in the organic mass.
The motion of solid bodies within machines and the motion of a machine relative to a fixed base are, inter alia, determined by the friction which is applicable in each case between the bodies concerned. The fundamental distinction must here be made as to whether the bodies slide on one another or roll on one another. The magnitude of the sliding friction depends on whether the bodies slide directly on one another or are completely separated from one another by a lubricant. This is called dry friction in the first case and hydraulic friction in the second. So-called semi-hydraulic friction occurs if the lubricating film is incompletely formed. Sliding friction also takes place always in rolling bearings between the rolling elements and their guide elements.
As is known, the lubrication processes in machines can be classified in two groups. In hydrodynamic lubrication, the load-bearing capacity in a lubricating film is produced in the form of a gap of relatively large dimensions. The friction is then primarily determined by the temperature dependence of the viscosity of the lubricant. In the case of elasto-hydrodynamic lubrication, a very small lubrication gap is formed from an initially linear or punctiform contact of two elastic bodies. The flattening in the so-called Hertz contact region, together with the increase in the viscosity of the lubricant with pressure, has the result that the solid bodies moving relative to one another hardly touch directly or not at all. In existing practice, very high pressures, in the range of 1 to 40 kbar, are necessary to produce sufficiently high viscosities. By comparison, the pressures applied in hydraulic devices are much too low to enable a substantial change in the viscosity of the hydraulic oil and hence also the motion sequences. The pressure conditions in lubricants and in hydraulic oils have been described (Dubbel, Taschenbuch fur den Maschinenbau, [Pocketbook for Machine Engineering], Springer-Verlag, Berlin).
It is elementary to minimize the frictional losses in bearings by selecting a suitable lubricant. A large number of liquid lubricants--these are organic compounds in most cases--are nowadays in use. It is likewise elementary to ensure a high frictional force by selection of the materials, if a clutch effect or braking effect is to be achieved. The possibility, in principle, of changing the function of a mechanical component by varying the viscosity--for instance, changing the function from that of a slide bearing to that of a clutch--is provided by electro-rheology. In this case, the viscosity in layers of colloidal solutions is varied by means of an applied electric field (J. E. Stangroom, Electro-rheological Fluids, Phys. Technol., volume 14, pages 290-296 (1983)).
Some organic compounds do not pass directly from the crystalline phase into the isotropic-liquid phase on heating, but pass through one or more additional phases within clearly defined temperature ranges. These phases have anisotropic physical properties, as are observed in crystals, but are at the same time fluid like ordinary isotropic liquids. The phases formed by molecules of elongate shape are also described as a rod-like or calamitic phase. As distinct from the completely disordered isotropic phase, a long-range order of the orientation applies in this case. In the nematic phases (abbreviated as N) of hitherto known low-molecular compounds, the molecules can freely rotate about their longitudinal axis. Closely related to the nematic phase is the cholesteric phase which is formed by optically active elongate molecules or is obtained by addition of optically active compounds to nematic compounds. For purposes of the present invention, chol
REFERENCES:
patent: 3597043 (1971-08-01), Dreyer
patent: 3876286 (1975-04-01), Deutscher et al.
patent: 4115310 (1978-09-01), Sato et al.
patent: 4622164 (1986-11-01), Eidenschink et al.
Merck Patent Gesellschaft mit beschrankter Haftung
Stoll Robert L.
Wu Shean C.
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