Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Heterocyclic ring compound; a heterocyclic ring is one...
Reexamination Certificate
1999-05-14
2001-02-27
Medley, Margaret (Department: 1714)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Heterocyclic ring compound; a heterocyclic ring is one...
C508S282000, C508S495000
Reexamination Certificate
active
06194359
ABSTRACT:
This application is a 371 of PCT/EP97/05166 dated Sep. 20, 1997.
Subject matter of the invention is an operational fluid for lifetime-lubricated combustion engines, which combines the properties of a lubricant and a cooling fluid and, based on its novel composition, exhibts considerable advantages relative to known motor oils. It is applied in combustion engines which are produced of conventional metallic materials, but primarily also in engines comprising ceramic parts.
Classic combustion engines comprise a multiplicity of main structural elements such as pistons, piston rings, piston bolts, connecting rods, connecting rod bearings, [cylinder] liners, crankshafts, crankshaft bearings, camshafts, valves, valve guides and valve gear elements, which move against one another at relatively high speed and in the process traverse considerable wear paths. These structural elements are typically produced of metallic materials such as cast iron, steel, aluminum, brass and bronze alloys and are therefore subject to wear typical for the system.
In order to keep the friction between the structural parts at a minimum and thus to hold the wear at a low level, the friction sites of these combustion engines are supplied with lubricants which are conventionally comprised of hydrocarbons, mineral oils or also synthetic oils. The valve gear, to be sure highly loaded tribologically but rather minimally by temperature and contaminants, is supplied from the same oil reservoir as the thermally highly stressed crank gear laden with combustion residues. The operating life and changing intervals of the oil are determined by the latter.
To fulfil the manifold lubrication tasks, additives are mixed into the motor oils, which are intended to enlarge the spectrum of the performance of the motor oil and which, each by itself or in combination, have to carry out highly specific tasks. A considerable portion of these additives serves for the purpose of protecting the metallic materials sliding one upon another against wear, corrosion or welding together (seizing up).
Up to 35 percent of the particle emissions of a diesel engine have their origin in motor oils. The same applies to the hydrocarbons in the exhaust gas of Otto engines. A considerable fraction of the particle emissions comprises non-combusting additives such as phosphor, sulfur, zinc or barium compounds and many others which not only increase the soot particle emission but also contaminate the exhaust gas catalysts, which become consumed and must therefore be replaced as soon as the value falls below the value of the effective minimum concentration in the basic oil.
More recent materials such as hard metals, monolithic and stratified ceramics, sintered ceramics, carbon and tribological coatings today permit, in connection with constructional measures, new solutions for lubricating the combustion engine with far lower lubricant consumption than occurs in conventional combustion engines produced of conventional metallic materials.
Since, in the case of combustion engines produced of newer materials, in the following referred to simply as “ceramic engines”, the surfaces of the parts sliding against one another are no longer of only a metallic nature, the lubricants required for them can dispense with all additives which are today intended to protect [these parts] against corrosion or to prevent at all cost the material contact of the surfaces sliding against one another. The significantly better wear resistance of the listed newer materials (some have no tendency at all to seize) permits a considerably greater portion of mixed friction than is possible in the case of conventional engines comprising metallic materials.
Under these mixed friction conditions—or even when running dry—through the partial omission of the wear-reducing fluid lubrication, subsequently material substitute functions become possible: the wear reserve required in the case of conventional engines and the low shearing is displaced from the lubricants into the surface of the materials sliding against one another.
Ceramic materials are distinguished by high degrees of hardness, high melting points, low density, low thermal expansion, reduced corrosion and high resistance under thermal and chemical stresses. Therefore formed parts comprising ceramic materials are increasingly used wherever metallic materials no longer are sufficient to [counter] the mechanical, thermal or chemical stresses. Primarily aluminum oxide (Al
2
O
3
), zirconium oxide (ZrO
2
), silicon nitride (Si
3
N
4
), silicon carbide (SiC), cubic boron nitride (BN), aluminum nitride (AlN) and boron carbide (B
4
C) are considered to be materials which in the future will be suitable materials and coatings for the production of components for combustion engines.
However, like the parts of other materials, ceramic parts are also subject to abrasion. It is therefore necessary to ensure through suitable lubricants in their case also that the friction is kept at a minimum. Formulations have been presented for the solution of the problem of ways in which material losses due to friction of ceramic formed parts can be sufficiently prevented. In the following some suggestions toward a solution are listed:
According to one suggestion different materials such as oils, additives, polymers, solid sliding means and soaps are to be worked into ceramic composite materials before the fabrication of the ceramic formed part, through which the finished formed part obtains self-lubricating properties. However, the mechanical properties of the ceramic materials are disadvantageously changed through this process.
According to a further process, the surfaces of ceramic formed parts are to be coated with differing materials such as metal films, solid sliding means or polymer films in order to increase the ability to slide of the surfaces. However, such surface coatings are already abraded after a short time under mechanical, thermal or chemical stress of the ceramic parts since their wear reserve is low so that they are only temporarily effective.
A further possibility is the application of known soluble antifriction additives to a fluid lubricant, for example a mineral oil, which until now has customarily been used for reducing the friction of metal surfaces on one another. However, these means are based on a specific reaction with the metal surface whose atoms are bound ionically or covalently and for that reason cannot successfully be used with ceramic materials since the additives are not adsorbed by the ceramic surface or do not react chemically with it.
It has furthermore been proposed to disperse solid sliding substances, such as graphite or molybdenum disulfide, in oils and to apply these onto ceramic surfaces. Such solid substances, however, lead to occlusions of filters and must, moreover, be used in large quantities in order to be effective. Furthermore, in the presence of fluids on a surface, solid lubricants cannot form a solid film so that this proposal also does not solve the problem of attaining a satisfactory reduction of the friction losses of ceramic engines.
It has already been proposed in WO-A 92/07923 to use a fluid containing a monomer in order to reduce the friction losses of ceramic surfaces. Initially the monomer does not polymerize in the fluid, however, the polymerization is initiated by the flash temperature between the surfaces sliding past each other. In this process a polymer film is formed directly on the stressed surfaces. Thereby the monomers are consumed relatively rapidly and the lubricant must frequently be replaced.
None of the proposals for a solution known until now have yet been able to solve satisfactorily the problem of the reduction of the friction losses of mechanically, thermally or chemically stressed ceramic surfaces which is a prerequisite for combustion engines which do justice to their use in practice and have a long service life. However, since a tribologically and materially optimized engine does not make concessions to operating life and mechanical efficiency, s
Beyer Ludwig
Gasthuber Herbert
Müske Heiner
Woydt Mathias
Fragol Schmierstoff GmbH & Co. KG
Medley Margaret
Wenderoth , Lind & Ponack, L.L.P.
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