DE3720714A1 - Thermal insulation system for embedded components carrying hot gases in internal combustion engines - Google Patents

Abstract

The invention relates to a heat insulation system for embedded components carrying hot gases in internal combustion engines. In order to be able to achieve effective heat insulation and hence carry hot gases in internal combustion engines of all types, the heat insulation system consists of individual interconnected pipe elements made of a material resistant to high temperatures, on which is arranged a body of insulating material comprising ceramic high-temperature fibres. This body of insulating material surrounds the internal lining made of material resistant to high temperatures. The pipe element is used together with the body of insulating material as a core in the casting of the component and remains in the component carrying the hot gases.

Description

The invention relates to a thermal insulation system for hot gases leading, cast components of internal combustion engines.

It is common in the prior art to attach components Internal combustion engines that carry hot gases, such as for example, the exhaust gases of the internal combustion engine at least partly to produce as cast components and for example to be attached to the engine block of the internal combustion engine. So is it is common, for example, the exhaust gases of the individual Cylinder with cast exhaust manifolds together and together to the connected exhaust duct to continue. These exhaust manifolds are in one Mold with the appropriate connection piece for the Introduction of the exhaust gases and with the outlet to Connecting the exhaust duct poured and then to the Internal combustion engine attached so that the connecting piece for the introduction of the exhaust gases of the individual cylinders with corresponding, in the respective cylinder heads trained exhaust ducts are aligned.

It is also known to the individual Exhaust / intake ports in the cylinder heads are trained with insulating inner linings too Mistake. These linings are said to be excessive Heating of the flowing through the cylinder head Coolant and thus overheating of the cylinder head prevent, but they should also prevent  Emission of pollutants into the atmosphere prevent the exhaust gases from behind the exhaust valves be kept at high temperature. If the temperature the exhaust gases are kept as high as possible those generally arranged in the exhaust system downstream units, the task of which Reduction of harmful exhaust gas components is with greater efficiency. This means not only the share of harmful emissions, but also fuel be saved.

In order to optimally embed the inner lining in the Exhaust channels of the cylinder head were to be obtained on the one hand tubular inserts known to the pouring the cylinder head into the remaining Exhaust ducts have been inserted. However, this is only if the exhaust ducts are relatively simple possible. If the course is more complicated or curved Exhaust ducts were also known to use such inserts Suitable to arrange in the mold of a cylinder head and then the cylinder head around these inserts to water. An example of such a technique is shown in DE-OS 36 07 911 described.

For the insulation of exhaust manifolds, that is Exhaust ducts of the individual cylinders outside the Cylinder heads continue and a common one Exhaust pipes have been used for thermal insulation Sheaths known in which the manifold after their Manufacturing have been embedded in the cast. The Attachment of such jackets, for example compared to the cylinder head is relatively cumbersome and moreover, the thermal insulation effect known sheaths limited.

The invention is based on this state of the Technology based the task of a thermal insulation system for cast gases from hot gases To create internal combustion engines that are simply realized can be an extremely high thermal insulation Has an effect on the exhaust gases passed through.

This task is solved with a thermal insulation system type mentioned by an inner lining individual, interconnected pipe elements a highly heat-resistant material and a ceramic Insulation body comprising high temperature fibers, which as Thermal insulation layer surrounds the pipe elements, the from Insulation body encased interconnected Pipe elements serve as the core when casting the component. With these features, it becomes possible to get complicated Forms of various types of such hot gases realizing leading components by accordingly molded pipe elements connected together and then with be encased in the insulation body. It can be thus, for example, exhaust manifolds for all engines Manufacture size and construction. The extremely good thermal insulation is achieved through the use of a ceramic Insulation body comprising high temperature fibers, which the then interconnected pipe elements in total encased, reached. As an insulation body, a Insulation body made of ceramic high temperature fibers of the Systems Al₂O₃ / SiO₂ can be used. The production of the insulation body, according to the shape required e.g. in the vacuum suction process with downstream thermal precision pressing. This is one Standard production in a reproducible setting possible.

Such an insulation body can take on the most complicated shapes  the gas routing components are adapted and serves the Pouring around as a core, which after the casting process in the cast component remains.

Such a ceramic insulation body largely prevents the heat transfer to the cast and thus water-cooled cylinder head walls and to the cooling water.

Due to the high temperature that the inner lining is made of the heat-resistant material through direct contact with the hot gases and because of the Maintains thermal insulation through such an insulation body, as an after-reaction an oxidation, i.e. a chemical Change from carbon monoxide to carbon dioxide and from Hydrocarbons to water and carbon dioxide favored. This will make the harmful Exhaust components significantly reduced. this happens especially if the exhaust gases are still sufficient Contain oxygen for a post-reaction. An insulation body using high temperature ceramic fibers offers compared to conventional insulation materials Oxide ceramics exist, not only the advantage that they are compared to such oxide ceramic parts in any shape and can be made with any cross-section, but also lead to a higher reduction in cooling effort in internal combustion engines, to a lower one Heat capacity, to a lower heat transfer, too higher thermal stability, better Noise reduction, to a higher one Exhaust emissions reduction, to a higher effectiveness Turbo Komprex charging, to a higher temperature level for emission control systems, for easier handling when pouring, for easier pouring also in Cast iron and finally to a higher one mechanical strength or durability.  

These advantages are also seen in an alternative Embodiment reached when the insulation body from a mixture of microporous silicon dioxide, ceramic fibers and opacifiers. A such material is called "Minileit" known and uses the principle of thermal insulation Microporosity, the heat conduction to the lowest theoretically possible dimension is reduced. The at Heat transfer through processes taking place such as heat conduction, gas convection, ultra-red heat radiation and molecular heat conduction through gases such an insulation body on the principle of microporosity all reduced to the lowest possible level. The Heat conduction over solid bodies is achieved by using Fabrics with extremely low thermal conductivity minimized, which are constructed in such a way that they are based on the A low solid cross section due to the heat conduction exhibit. Gaseous convection is minimized in which the cavity cells are kept sufficiently small so that convection currents cannot arise. For this becomes an extremely fine powder made of amorphous silicon dioxide used, which is suitably shaped and solidified, so that an extremely small cavity size is created. These Cavity size is smaller than the average free one Path length of the air molecules.

To reduce the infrared radiation, the Insulated body Minileit described as an opacifier High temperature metal oxides of a special particle size and distribution.

The heat conduction is also ultimately reduced that the distance of the cell walls in this  Material smaller than the mean free path length of a Air molecule, i.e. less than 0.1 µm below Realized normal conditions.

Another advantage of an insulation body, the ceramic Includes high temperature fibers is that the Possibility is created instead of the usual Gray cast iron, the components previously used in hot gases had to be used now, like that already with Motors is common to use aluminum as a casting material. For engines with very high exhaust gas temperatures, e.g. at High-performance engines, you had to go beyond one higher alloy casting material for the hot gases use leading components. Through the thermal insulation with a ceramic high temperature fiber Insulation body can now also be simpler for these purposes Cast iron or cast aluminum can be used.

Form in a possible embodiment of the invention the individual pipe elements where they join are pluggable interconnectable. As Plug-trained joints between the individual pipe elements create a certain balance of thermal expansion paths that the pipe elements experience when the hot exhaust gases are passed through. Tensions within that formed by the tubular elements Channel systems are avoided. The production of longer lines is extremely easy to do by using the Pipe elements in one of the outer contours of the desired Arranged component corresponding mold and then be cast around.

The way the connector between each Pipe elements can be reached, can be different. So can be provided, for example, the individual  Pipe elements at the ends forming the joints one end as a plug part and at the other end as Train socket part. By sticking in a row long lines can then be used put together. The individual pipe elements are according to their intended use for example equipped with connecting pieces, which then in the case of exhaust manifolds accordingly on the fit the corresponding socket on a cylinder head. So can, for example, a single one for each cylinder Pipe element can be provided, which then with the others Pipe elements of the other cylinders are put together and so forms an exhaust manifold. For a four-cylinder would then e.g. four pipe elements used while for a six cylinder six pipe elements can be used would.

In another embodiment, the connector thereby causing the individual pipe elements on their the ends forming the joints are the same and that intermediate rings are provided over which the successive ends of the tubular elements can be plugged on are. The pipe elements at their ends in Diameter to be slightly expanded, so that the intermediate rings when plugging together at the junction of the Pipe elements can be added without a step-shaped Section inside the pipe elements to form what a would counteract uniform gas flow.

In another embodiment, the individual Pipe elements welded together and there are in Course of a pipe elements welded together formed conduit voltage and Expansion compensation elements provided. Such Strain compensation elements can be used as metal bellows  be realized. To a in the area of the metal bellows elastic sheathing with the help of an insulation body ensure in this area of Insulation body in the form of a grid quilted ceramic nonwoven can be used. The stitching creates a certain elasticity of the Insulation body reached. The nonwoven can be made from one Al₂O₃ / SiO₂ fleece exist.

The tubular elements forming the inner lining can be from metal parts manufactured using the deep-drawing process high-temperature resistant stainless steels. As Stainless steel, for example, comes in an Inconel steel Nimonic steel and similar stainless steels in question.

Before pouring the interconnected and with one This has to be the case with tubular elements covered with damping material formed component are annealed for degassing. The subsequent casting process itself can be done directly better perform the insulation material around when the Insulation body has no other outer skin. The The insulation body can then degas better and it can be created no problems with gasing during casting. However, this can lead to shrinkage of the Insulation body and thus shape changes come what can only be accepted if it is on the Dimensional accuracy of the coated tubular element in the finished cast component does not arrive, i.e. when large Dimensional tolerances are permitted. However, if a high one Dimensional accuracy is required, it is an advantage To coat the insulation body with an outer skin. The outer skin can also consist of an Inconel steel. It can but also be provided as a so-called outer skin. Ceramic fiber coating, for example from a colloidal Use SiO₂ with a ceramic fiber matrix. Such one  Coating has an adhesive property and possesses it also the advantage that no additional steel outer skin must be provided. The mass for one Ceramic fiber coating is in contrast to known kittens and mortar is relatively light and is stretchable and vibration behavior optimally on the fiber materials of the insulation body. This coating can be on the insulation body is simply sprayed on.

The invention also claims protection for a single pipe element with the characteristics of the one such pipe element directed claims.

The invention is based on the in the Drawing illustrated embodiments further explained and described.

Fig. 1 shows the overall view of the assembled from individual tubular elements inside liner for an exhaust manifold which is, however, not yet cast in,

Fig. 2 shows a view in the direction of arrow II of Fig. 1 on the exhaust manifold with casting and embedded inner lining,

Fig. 3 is a sectional view of detail D of FIG. 1,

Fig. 4 is another embodiment of the detail D in Fig. 1,

Fig. 5 is another embodiment of the detail D in Fig. 1,

Fig. 6 is also another embodiment of the details D of FIGS. 1 and

Fig. 7 shows an exhaust manifold with welded pipe elements and with a metal bellows for expansion compensation.

In Fig. 1, the thermal insulation system according to the invention is shown using the example of an exhaust manifold, hereinafter referred to as a manifold pipe. The thermal insulation system forms an inner lining, which is designated as a whole by 1 . As will be explained further below, this inner lining is cast around after the individual elements have been plugged together in order to produce the finished manifold tube. The cast jacket is not shown in FIG. 1, but can be seen in FIG. 2.

As can be seen, the interior lining shown is suitable for an exhaust manifold of a six-cylinder internal combustion engine. The inner lining consists of six individual, nested pipe elements 2 to 7 . Each pipe element has a connecting piece 2 a to 7 a . These connecting pieces 2 a to 7 a are aligned with exhaust channels, not shown, in the respective cylinder heads of the internal combustion engine.

The pipe element 2 is provided with an outlet nozzle 2 b , to which an exhaust pipe can be connected for passing on the collected exhaust gases.

The pipe elements form butt joints at the lines labeled S , at which they are pluggably connected to one another. After plugging together, the then finished inner lining is placed in a casting mold and the outer casting jacket of the header pipe is then produced. The tube elements serve as a core in the casting mold during this casting process. After the casting, the tubular elements are firmly embedded in the mold, as shown in FIG. 2 in view II of FIG. 1. There, the cast jacket is provided with the reference number 8 and has suitable connections, for example bores 9 , in order to be able to produce the further connections.

The structure of the individual tubular elements is shown in a first embodiment in FIG. 3. There the joint between the tubular element 5 and the tubular element 6 is shown in detail, for example. The other joints S are each designed accordingly in the further embodiment variants. The inner wall 10 of the tubular elements 5 and 6 (and also the other tubular elements) consists of an Inconel steel 600 , for example with a thickness of 0.45 mm. An insulation body 11 in the form of a ceramic fiber material is applied to the surface of the inner wall 10 not facing the exhaust gas routing side. This material completely surrounds the inner wall 10 , ie also in the course of the individual connecting pieces 5 a or 6 a etc.

The thermal insulation layer formed by this insulating body 11 is embedded in an outer skin 12 , which in the case of the exemplary embodiment according to FIG. 3 also consists of Inconel steel 600 . However, the steel is thinner than that of the inner wall 10 and its thickness is approximately 0.2 mm.

These tubular elements constructed in this way are produced by prefabricating the inner wall 10 and the outer skin 12 using the deep-drawing process. As can be seen, the joints in this exemplary embodiment are designed in such a way that the tubular element 5 is designed as a plug part on its side facing the tubular element 6 , while the tubular element 6 serves as a socket on this side. To this end, the tubular element 5 initially passes in a step 15 into an axially parallel section 16 and from there into a slope 14 towards the end 13 . In the last section 17 , the outer skin 12 is connected directly to the inner wall 10 , so that the insulation body 11 is completely embedded. The inner wall 10 of the tubular element 6 is designed as a bushing corresponding to the described course of the outer skin 12 . In the area of the horizontally running sections 16 and 17 there are overlap areas which allow a possible displacement of the tubular elements 5 and 6 relative to one another in the axial direction, without thereby giving up the sealing effect at the joint. Due to the design of stage 15 and stage 18 , the tubular elements can be put together in such a way that projections are formed neither towards the outer surface nor towards the inside, which comes into contact with the exhaust gases.

Another possible configuration of the joints S is shown in FIG. 4. In this variant, the insulating body is embedded at the end in each case by vertically extending portions 19 and 20 over which the outer skin passes 12 in contact with the end portion of the inner wall 10 and the inner wall of the tubular element 6 in contact with the outer skin 12th

To the hot gas-carrying inside, the design is also made so that there are no edges that protrude into the line. The tubular element 6 forms an overlap area with the outer surface around which the casting is cast, which, in contrast to the embodiment in FIG. 3, projects beyond the surface of the outer skin 12 of the tubular element 5 .

In the cases of FIGS. 3 and 4, the outer skin consists, as mentioned, of a thin steel sheet.

In the embodiments of FIGS. 5 and 6, however, the outer skin of a ceramic fiber-coating material. This outer skin is provided with the reference number 21 . In order to be able to embed the insulating body 11 in these exemplary embodiments, the end regions of the tubular elements are each of the same design. In the embodiment according to FIG. 5, the inner wall 10 merges via a step 22 into a section of larger inner diameter and is bent at the end by a section 23 pointing transversely to the pipe axis upwards over the full height of the insulating body 11 . As a result, the insulating body 11 is also embedded. The plug connection is made with the help of an intermediate ring 24 , which extends approximately equally in both sides into the adjacent pipe elements. The ends of the tubular elements are pushed onto this intermediate ring 24 . Between the ends formed by the vertical section 23 , a sealing ring 24 is arranged, which also consists of a ceramic fiber insulating material and also prevents heat dissipation or heat transfer in this area.

The embodiment according to FIG. 6 differs from the embodiment according to FIG. 5 in that correspondingly designed sections 25 and 26 are used to form the vertical sections 23 . The section 25 is placed on the inner wall 10 so that the vertical section 23 projects beyond the end 27 of the inner wall 10 of the tubular element 5 , while the section 26 on the tubular element 6 is set back relative to the end 28 of the inner wall 10 of this tubular element. Thereby, the portion with slides when nesting the end 28 of the tubular element 6 of the tubular member 25 5, so that also a plug-in connection is formed. Between the two vertical sections 23 there is again a sealing ring 24 made of ceramic fiber material.

In all cases, joints are formed that it allow the pipe elements to fit into each other, before the casting is made.

In the exemplary embodiment shown in FIG. 7, a section from a hot gas-carrying component is shown, which is also equipped with the thermal insulation system according to the invention.

The component is again shown only in sections, three interconnected pipe elements 2 ', 3 ' and 4 'can be seen.

The pipe elements 2 'and 3 ' are welded together at their joint S in the region of their inner wall 10 . This inner wall is in turn made of a high-temperature stainless steel. Between the tubular elements 3 'and 4 ' a metal bellows 30 is arranged for expansion and stress compensation, which is welded at its ends to the corresponding ends of the tubular elements 3 ', 4 '. The inner wall 10 is in turn covered with an insulating body 11 of the type described. In the area of the metal bellows 30 , the sheathing 11 'consists of a ceramic fiber fleece which is quilted in a grid pattern with stitching 31 . Due to the design of the insulating body as a non-woven fabric 11 'in the area of the metal bellows 30 , elastic insulation is achieved in this area, that is, the fleece 11 ' can carry out the stretching of the metal bellows without causing leaks.

The thermal insulation layer formed by the insulating body 11 and the fleece 11 'is in turn surrounded by an outer jacket 21 . This outer jacket can either be a steel jacket or a ceramic fiber coating material. This material ensures the dimensional accuracy after the casting process and still allows gases to pass through, so that sufficient degassing can take place when the component is tempered before casting.

The entire component, which, as mentioned in FIG. 7, is shown only in sections and in simplified form, is then provided with the casting 8 .

The pipe elements interconnected according to the invention form a thermally insulated component that is extremely good has heat-insulating properties. It is clear that with such a thermal insulation system the most different Let shaped pipe elements connect with each other, see above that you can line pipes for hot gases of any shape and can generate any length.

The invention is also directed to a single tubular element which has a layer structure, as can be seen in FIGS. 1 to 7. Such pipe elements can be used not only in exhaust manifolds or manifold pipes for exhaust gases from internal combustion engines, but also in all hot gas-carrying components, such as exhaust / inlet channels, piston bowls, prechambers and swirl chambers of internal combustion engines, these pipe elements then being poured into the corresponding components Molds are inserted and then cast.

Claims (19)

1. Thermal insulation system for hot gases leading, cast components of internal combustion engines, characterized by an inner lining of individual, interconnected tubular elements ( 2 , 3 , 4 , 5 , 6 , 7 ; 2 ', 3 ', 4 ') made of a high-temperature resistant material ( 10 ) and by a ceramic high-temperature fiber insulating body ( 11 , 11 '), which surrounds the inner lining ( 10 ) of the tubular elements as a thermal insulation layer, the interconnected tubular elements of the insulating body ( 11 , 11 ') serving as the core when casting the component . 2. Thermal insulation system according to claim 1, characterized in that the insulating body ( 11 , 11 ') consists of ceramic high-temperature fibers of the system Al₂O₃ / SiO₂. 3. Thermal insulation system according to claim 1, characterized in that the insulating body ( 11 ) is formed from a mixture of microporous silicon dioxide, ceramic fibers and opacifiers. 4. Thermal insulation system according to one of claims 1 to 3, characterized in that the individual pipe elements form joints ( S ) at which they can be plugged together. 5. Thermal insulation system according to claim 4, characterized in that the individual pipe elements ( 2 , 3 , 4 , 5 , 6 , 7 ) are formed at their ends ( S ) forming ends at one end as a plug part and at the other end as a socket part. 6. Thermal insulation system according to claim 4, characterized in that the individual tubular elements ( 2 to 7 ) at their ends ( S ) forming ends are the same and that intermediate rings ( 24 ) are provided, via which the mutually facing ends can be plugged. 7. Thermal insulation system according to at least one of claims 1 to 3, characterized in that the individual tubular elements ( 2 ', 3 ', 4 ') are welded together. 8. Thermal insulation system according to claim 7, characterized in that tension and strain compensation elements ( 30 ) are provided in the course of an interconnected pipe elements ( 2 ', 3 ', 4 '). 9. Thermal insulation system according to claim 8, characterized in that metal bellows ( 30 ) are provided as tension and strain compensation elements. 10. Thermal insulation system according to claim 9, characterized in that the metal bellows are coated with thermal insulation material ( 11 ') in the form of a quilted, ceramic fiber fleece in grid form. 11. Thermal insulation system according to at least one of the preceding claims, characterized in that the inner lining ( 10 ) made in the deep-drawing process metal parts made of heat-resistant stainless steels such as Inconel, Nimonik. 12. Thermal insulation system according to at least one of the preceding claims, characterized in that the insulating body is coated with an outer skin ( 12 , 21 ). 13. Thermal insulation system according to claim 12, characterized in that the outer skin ( 12 ) consists of a heat-resistant stainless steel, in particular Inconel steel. 14. Thermal insulation system according to claim 12, characterized in that the outer skin ( 21 ) consists of a fiber mass (ceramic fiber coating) which is applied to the insulating body ( 11 ) for gluing it together. 15. Pipe element for guiding hot gases on internal combustion engines consisting of an inner lining ( 10 ) made of a high-temperature stainless steel and an insulating body ( 11 ) arranged thereon made of a material comprising ceramic high-temperature fibers. 16. Pipe element according to claim 15, characterized, that the insulation body made of ceramic High temperature fibers of the Al₂O₃ / SiO₂ system. 17. Pipe element according to claim 15, characterized in that the insulating body ( 11 ) is formed from a mixture of microporous silicon dioxide, ceramic fibers and opacifiers. 18. Pipe element according to at least one of claims 15 to 17, characterized in that the insulating body is surrounded by an outer skin ( 12 , 21 ). 19. Pipe element according to claim 18, characterized in that the outer skin consists of a fiber mass (ceramic fiber coating), which is applied to the insulation body ( 11 ) for gluing it together.