Internal-combustion engines – Combustion chamber – Having coating or liner
Patent
1988-02-09
1989-09-05
Wolfe, Willis R.
Internal-combustion engines
Combustion chamber
Having coating or liner
123188AA, 123193P, F02B 7702, F02F 312
Patent
active
048628654
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a insulating material for thermal insulation of components exposed to combustion gases in an internal combustion engine. The invention also relates to a method of thermally insulating a surface of an engine component.
It is a known fact that by thermally insulating components in combustion engines, such as pistons, combustion chamber walls, valves and exhaust ducts with an insulating material with a lower coefficient of thermal conductivity than the metal in the components it is possible to shift the heat from the cooling water to the exhaust gases. The dimensions of the radiator and water pump for example can thus be reduced and a certain increase in engine efficiency can be achieved, especially in combination with a so-called turbo compound, in which case an increase on the order of 5% can be achieved.
Various ceramic materials having a low coefficient of therml conductivity have for example been used as insulating materials in this context. The problem with ceramic material is, however, that they are brittle and break easily during assembly and engine operation. Furthermore, it is difficult to get the ceramic material to bond to the metal substrate due to the relatively large differences in thermal expansion coefficient between the metal and the ceramic.
In order to avoid the problems accompanying the use of ceramic insulating materials in engines, the use of a purely metallic insulating layer has been suggested, consisting of metal nets sintered together to form a porous layer. A thin metal platee of stainless steel is sintered or soldered to the net layer consisting of nets to form a tight corrosion resistant, heat resistant surface layer. The insulating layer as a whole can be soldered to the engine component or placed in its mold and bonded to the component as the component is cast.
The use of such an insulating layer has its limitations, however, in that it cannot be machined. In certain locations in an engine, the tolerances between the various components, e.g. between the top of the piston and the cylinder head in a diesel engine, are narrower than the castoing tolerances. The former can be fractions of a millimeter while casting tolerances of less than ca 1.5 mm are difficult to achieve in practice.
The purpose of the present invention is to achieve a metallic insulating material which does not have the above-mentioned practical limitations.
This is achieved according to the invention in that the material comprises an insulating layer of porous sintered metallic powder.
In normal production of sintered components, the pressure used before sintering is so high that the porosity does not amount to more than a few percent of the volume. As a rule, one tries to achieve a porosity which is as low as possible and residual porosity after sintering is then not something which is desirable. When producing the insulating layer according to the invention, however, a lower compression pressure is used which results in a porosity of up to about 50%. This gives a coefficient of thermal conductivity which approaches the coefficient of the ceramic materials which have been used for the same purpose.
The sintered insulating layer can be machined in the same steps as the engine component which is the substrate. Not only does this provide the component with the desired shape and dimensions, but the surface pores of the sintered layer are to a great extent sealed.
The invention will be described in more detail with reference to an example shown in the accompanying drawing, in which
FIG. 1 shows a section through a portion of a piston and
FIG. 2 is a section through a portion of a mold for casting the piston in FIG. 1.
The piston shown in FIG. 1 has a cast metal body 1. The upper surface 2 of the metal body is in the embodiment shown completely flat, as is common practice in petrol or gasoline engines, but it could just as easily have been made with the depression in the upper surface of the piston which is characteristic for direct injection diesel engines.
The entire upper surface
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patent: 4646692 (1987-03-01), Deuber et al.
patent: 4694813 (1987-09-01), Mielke
Dahlen Lars M. G.
Larsson Lars E.
Othzen Bo L. A.
AB Volvo
Wolfe Willis R.
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