WO1997012130A1

WO1997012130A1 - Exhaust manifold

Info

Publication number: WO1997012130A1
Application number: PCT/EP1996/003981
Authority: WO
Inventors: Detlef Hotschicke; Olaf Schmenkel; Dieter Wagenplast; Gerhard Walter
Original assignee: Elring Klinger Gmbh
Priority date: 1995-09-28
Filing date: 1996-09-11
Publication date: 1997-04-03
Also published as: DE19536124A1; EP0852663A1

Abstract

In an exhaust manifold (10) for the exhaust system of an internal combustion engine, with a pipe (12) forming the inner side of a manifold and having at least one stub (14 to 17) for connecting to at least one combustion chamber of the engine and with a heat insulating layer (18) fitted around the pipe (12), it is proposed that the heat insulating layer (18) be made from a very fast-curing moulding compound comprising a high-temperature-resistant binder, a particulate component of a porous material and a fibre or needle-shaped reinforcing component and that the heat insulating layer (18) as such form the outer surface of the exhaust manifold (10), so that the exhaust manifold (10) is able to withstand the hard conditions in the engine compartment of a motor vehicle, has a low heat capacity and nevertheless has an outstanding insulating effect.

Description

Exhaust manifold

The invention relates to an exhaust manifold for an exhaust system of an internal combustion engine with a tube forming the inside of the manifold with at least one connecting piece for connection to at least one combustion chamber of the internal combustion engine and with a thermal barrier layer arranged around the tube.

Exhaust manifolds of this type in most cases include a pipe designed as a branch pipe or manifold with a plurality of connecting pieces for connection to a plurality of combustion chambers of the internal combustion engine.

The generally customary exhaust manifolds are manufactured as solid cast components. These cast components become quite hot during operation of the engine and radiate heat into the engine compartment.

Another problem of the solid cast component as an exhaust manifold is that this component has a relatively high heat capacity, so that the cast component cools the exhaust gas very strongly over a longer period of time, especially when the engine is started. During this time, the exhaust gas has a temperature which is too low in order for the exhaust gas catalytic converter to function within a shorter time, i.e. to be able to heat up to the necessary operating temperature. The heat loss of the entire exhaust system up to the catalytic converter is often so great, especially in engines with low fuel consumption, even in normal operation, that at low engine speeds, for example at idling speed, a sufficiently high temperature cannot be maintained in the exhaust gas catalytic converter, so that the cleaning performance of the catalyst drops rapidly under such operating conditions.

The attempt is made to counter the insufficiently high temperatures in the exhaust gas catalytic converter in that the exhaust gas catalytic converter Provides the analyzer with an electrically operated or fuel-operated heating device, which should quickly bring the catalytic converter up to operating temperature, particularly in the start-up phase. This increases the control effort in the catalytic converter not inconsiderably. In addition, the production costs of such catalysts are also significantly higher than those of the unheated ones.

In order to counteract the problem of excessive heat radiation, a double-walled exhaust manifold was developed, which consists of two thin-walled steel tubes with an air gap enclosed between them. Alternatively, this air gap can also be filled with an insulation material.

The heat capacity of this exhaust manifold is reduced by the reduction in the metallic mass, although the manifold is very expensive to manufacture and moreover very complicated to manufacture. Furthermore, the insulation effect of the double-walled exhaust manifold is inadequate in many applications.

A similar solution is known from DE-24 03 998-A1, in which a thermal insulation layer is applied to the steel pipe of an exhaust manifold, which in turn is covered with a housing. The aim of this embodiment of the exhaust manifold is to reduce the heat radiation and noise in the engine compartment, ie ultimately to encapsulate the exhaust manifold. The heat insulation layer is completed together with the housing half-shells and can be connected in this prefabricated state to the steel pipe of the exhaust manifold, so that, in addition to simple assembly, various other assembly problems are solved. The disadvantage of this solution is the complicated structure of the thermal insulation material and the necessity of a housing, which overall means a high manufacturing effort.

The object of the present invention is to propose an exhaust manifold which can cope with the harsh conditions in the engine compartment of a motor vehicle, has a low heat capacity and nevertheless has an excellent insulation effect.

This object is achieved according to the invention in that the thermal barrier coating is formed from a curable molding compound which comprises a high-temperature-resistant binder, a particulate component of a porous material and a fibrous or needle-shaped reinforcing component, and in that the thermal barrier coating as such comprises the outer surface of the exhaust manifold forms.

With such a thermal barrier coating, the curable molding compound can represent the outer surface of the exhaust manifold itself and does not require an additional housing, which not only reduces the weight of the exhaust manifold, but also further reduces the thermal capacity of the exhaust manifold.

In some applications, for example as protection against mechanical damage caused by stone chips, etc., an additional sheet metal casing to increase the durability can be desired.

With the curable molding compound to be used according to the invention, a self-supporting component element can be obtained which on the one hand has sufficient strength to meet the difficult operating conditions in the engine compartment and moreover to ensure the actual stability of the exhaust manifold. In view of this, the inner tube of the exhaust manifold can also be reduced in terms of the material thickness to a thickness which still withstands the chemical and thermal stress caused by the combustion gases flowing out of the combustion chambers, with mechanical stability, in particular vibration resistance of the component that takes the thermal insulation layer as such into account.

An inorganic reaction mixture forming a ceramic matrix is preferably used as the binding agent in the exhaust manifold according to the invention. Thermal insulation layers from these reaction mixtures can later be easily removed with household waste or can be recycled in the course of the production of new thermal insulation layers. The use of a purely inorganic formulation also ensures very environmentally friendly production.

Inorganic reaction mixtures which are cold-curing are preferably used, since for such molding compositions the tools can be made from wood or plastic, which avoids the production of expensive metal casting molds. Inorganic reaction mixtures which are suitable for this are self-curing and at most give rise to temperatures of up to 80 ° C. in the curing reaction.

Binder systems which are particularly suitable in this sense are described, for example, in DE-40 40 180-A1. The molding compositions described there - with or without foaming agents - are not suitable as molding compositions for the present invention, since the molded parts produced in this way would not be able to withstand the mechanical stresses in a motor vehicle, but it has surprisingly been found that these Shape- compositions according to DE-40 40 180-A1 are well suited as a binder system for the present invention.

A preferred inorganic reaction mixture contains water glass, potassium hydroxide solution and furnace filter dust from the corundum production. This dust arises when bauxite is melted in large furnaces, whereby at temperatures of approx. 2000 "C, fine particles as well as evaporated and re-condensed material are whirled up due to the resulting thermals.

This dust is then collected in the suction filters. The chemical composition, depending on the raw material used (bauxite), is approximately

50-70% by weight of Al2O3

20-70% by weight SiO 2 and additions of TiO 2

Fe ₂ 0 _3r

CaO, MgO, Na ₂ 0,

K ₂ 0

and possibly other trace elements.

The grain size of this filter dust varies in large ranges from approximately 0.1 μm to approximately 200 μm. The curing time can be set in a wide range, for example between 5 seconds and 1 hour, by adding the potassium hydroxide solution. This creates the opportunity to optimize the curing time. adapt to the existing manufacturing possibilities and the related manufacturing cycles.

Sodium water glass is preferably used as the water glass, since this is not only cheaper than potassium water glass, but also offers the advantage that the ceramic matrix formed has a higher mechanical strength and greater temperature resistance.

The self-curing inorganic reaction mixture, which forms a ceramic material, is preferred in particular because it forms a matrix which has a comparable strength to sintered ceramic.

In order to accelerate the hardening process of the inorganic reaction mixture forming the ceramic matrix, heat hardening can be carried out at about 70 to 80 ° C. Higher temperatures are less desirable since in many cases this would require the use of metal moldings.

No particular requirements are initially to be made of the particulate component made of porous material except that it has the lowest possible thermal conductivity and, moreover, also the lowest possible thermal capacity. In particular, the particulate component need not have any particular mechanical strength, in particular, it does not have a high compressive strength, and the particulate component does not require high thermal stability either. In the event that there is a change in the particulate component at the high temperatures prevailing in the engine compartment, in particular as a result of the exhaust gases from the combustion chambers flowing through the exhaust manifold, this essentially leaves the function of the thermal barrier coating Unaffected, since the matrix of the high-temperature-resistant binder surrounding the individual particles ensures the dimensional stability of the thermal insulation layer and also prevents any defects that may form within the matrix from forming larger cavities, so that even in the worst case, when the particulate particles are destroyed As a result of the temperature effect of the combustion chamber exhaust gases, a structure of the thermal insulation layer in which a large number of cavities serving for thermal insulation is preserved.

However, preference is given to using particulate, pore-containing materials, in particular in granular form, which also withstand the high-temperature conditions of the exhaust manifold, preference being given here to hollow glass spheres, expanded glass, vermiculite and / or pearlite.

The use of expanded glass or foamed glass instead of hollow glass spheres poses no problems, since the closed porosity of the hollow glass spheres is not necessary for the particulate, porous component and the open porosity of the expanded glass particles is not disruptive in view of the normally set toughness of the molding composition ¬ works. Expanded glass is also much cheaper than hollow glass spheres. Vermiculite and pearlite particles are preferred materials because of their very low density, whereby vermiculite can also be selected as a particulate component due to its layer structure from the point of view of an improved acoustic insulation effect.

In addition to the thermal insulation properties of the particulate, pore-shaped material, the possibility is used as a side effect that the molded parts have a relatively low specific To produce density which is preferably <2 g / cm ³ , more preferably <1.5 g / cm ³ . Insulation layers with such a low specific density can be used to a large extent for thermal insulation not only directly on the exhaust manifold, but also in the continuation of the exhaust pipe in the entire exhaust system, without causing weight problems in motor vehicle construction.

A wide range of reinforcement materials are also available for the reinforcement component, wherein fibrous reinforcement components are not only individual fibers, but also non-woven fabrics, fiber fabrics, knitted fabrics or the like. Likewise, needle-shaped reinforcement components are also to be understood as needle fleece or the like.

However, the needle- or fibrous reinforcing component is preferably mixed into the molding composition in the form of individual fibers or individual needles, which does not exclude that more or less large agglomerations of individual fibers and individual needles can occur in the molding composition. Needle-shaped wollastonite, glass fibers, mineral fibers, mineral wool and / or metal fibers have proven to be particularly suitable.

The needles or fibers of the reinforcement component should preferably have a length in the range from approximately 50 to approximately 200 μm. The lower limit of approx. 50 μm results from the fact that no reinforcing effect is achieved to a sufficient extent in the case of significantly shorter fibers, while the mixing of the molding composition becomes problematic in the case of fibers with a significantly greater length than 200 μm and breaking of the long ones Fibers are to be feared in the production of the molding compound. An exception to this are glass and metal fibers, which can be up to approx. 15 mm long.

In addition to the previously described essential components of the molding compound for the production of the exhaust manifold according to the invention, the molding compound may optionally contain, for example, a filler which can either be used to improve the properties of the molded parts or simply to reduce the cost of the molding compound material.

Talcum powder, for example, is a preferred filler, since its platelet structure improves the elasticity of the hardened molding material or the thermal insulation material.

Mica can also be used as a filler and is valued for its high heat resistance.

Lime forms a particularly inexpensive filler, which is used in particular as a substitute for stretching the molding composition.

However, hardened and shredded thermal insulation material itself is also suitable as fillers for newly produced molded parts or thermal insulation layers. In this way, used thermal insulation layers can be completely reused and do not have to be disposed of with the household waste.

In the case of the fillers, care is preferably taken to ensure that the size of the filler particles ranges from approximately 0 to approximately 100 μm, with the largest possible particle size distribution. This means that a very narrow distribution within the range up to 200 μm grain size is preferably avoided. The molding composition may also contain inorganic pigments, in particular in the form of metal oxides, such as iron oxides, chromium oxides etc.

The viscosity of the molding composition is preferably set to a viscosity of <150 Pas, regardless of the type of binder used. This not only permits good processing of the molding composition, but also permits gentle mixing in of the fibrous or needle-shaped reinforcing materials or a correspondingly simple soaking and / or coating of the fiber and / or needle felt used.

The advantages of the exhaust manifold according to the invention are, in particular, that they do not necessarily require a supporting structure made of sheet metal parts on the inside and can be produced in almost any configuration by means of molds which are easy to produce. In the exhaust manifold according to the invention, the presence of an inner metal tube is not excluded. In particular, thin steel tubes can be used here.

The heat capacity of the exhaust manifold according to the invention is extremely low and thus ensures that the catalytic converter starts up quickly. Due to the excellent insulation effect of the thermal insulation layers, a low heat emission to the engine compartment is achieved. In addition, the low weight of the exhaust manifold according to the invention and the low manufacturing price are impressive.

In addition, a particularly smooth surface can be achieved in the components and thus an upgrading of the optical Achieve the appearance of the component. This is of particular importance in the current tendency of automobile manufacturers to strive for an attractive design of the engine compartment.

In addition, it is also easily possible to make the surface of the exhaust manifold acoustically favorable, e.g. through a waffle or honeycomb structure.

Because of the high stability of the thermal insulation layer, it resists all the usual influences which normally occur in the engine compartment, so that an extra housing for encapsulating the exhaust manifold can be dispensed with.

In particular, the use of corundum furnace filter dust, in conjunction with a recipe to be described in detail, permits hardening so quickly that large-series production is possible (for example 160,000 parts per mold and year and more).

The tube forming the inside of the elbow, in particular branching tube, is preferably a sheet metal part, in particular a sheet steel part.

Alternatively, the tube can also be designed as a ceramic component. The wall thickness of the pipe, in particular of the branch pipe, is preferably <2 mm, ie the wall thickness of the pipe is reduced to the extent that this is necessary with regard to the required stability to the exhaust gases emerging from the combustion chambers of the internal combustion engine. is justifiable.

The stability of the exhaust manifold is essentially ensured by the thermal insulation layer, while the tube forming the inside of the manifold protects the thermal insulation layer from chemical and direct thermal loads on the exhaust gas coming from the internal combustion engine.

The thermal barrier coating is preferably built up in such a way that the fibrous component is used as a high-temperature-resistant fiber mat with a pore volume, the pore volume of the fiber mat being partially filled with the curable molding compound.

In this case, the fiber mat is preferably only impregnated on its outer layers, preferably with a layer thickness of <2 mm. The thickness of the fiber mat itself is usually in the range between approximately 5 and approximately 20 mm, preferably in the range from 6 to 15 mm, typically approximately 10 mm.

When using fiber mats with a pore volume, the grain size of the particulate component is selected so that it is possible for these particles to penetrate into the surface layers of the fiber mat. This allows the curable molding mats to penetrate completely into the surface layers without separation of the binder and the particulate component. As an alternative to the use of the fiber mats, it can be provided that the molding compound contains the reinforcing fibers or needles essentially individually and is foamed. Scattered and distributed reinforcing fibers are also understood to mean those fiber components which are slightly agglomerated but not connected to form a nonwoven.

The heat insulation layer can be made in several parts and is then preferably designed to be removable from the tube forming the inside of the elbow. In the event of a repair, the thermal insulation layers can thus be removed from the tube forming the inside, exchanged and re-equipped with the thermal insulation layer parts.

The parts of the thermal barrier coating can be preformed. Alternatively, it is also possible to form the parts of the thermal barrier coating itself on the tube forming the inside of the elbow.

Alternatively, it can be provided that the thermal insulation layer is molded onto the branch pipe and forms a unit with it.

The invention further relates to an exhaust system for an internal combustion engine, which comprises an exhaust manifold of the type described above.

In this exhaust system, further lengths of pipe are preferably covered with a heat insulation layer, such as that which corresponds to the heat insulation layer described for the exhaust manifold specified above. In the fiber mat described above, a mat is preferably used, the pore volume of which makes up approximately 95 volume percent of the total volume of the fiber mat. The impregnation of the fiber mat is preferably carried out in such a way that the outer layer of the fiber mat is soaked 100%, ie the pore volume is reduced to zero, while the inner region of the fiber mat is only about 30% of its size Pore volume is filled. The thickness of the 100% filled layer is approximately 10 to 20% of the total thickness of the fiber mat.

Preferred fiber mats have a drawn fiber diameter of approximately 6 to approximately 8 μm, so that the fibers are not respirable. The fiber mats are preferably free of ceramic fibers and also free of binders. The mats should have a particularly good needling in the direction of the mat thickness. The fiber mat must have good tensile strength in all directions.

In addition, the mats should be easy to adapt spatially to the branching pipe of the exhaust manifold and, in addition to good temperature resistance, should also be vibration-resistant. It is important with regard to the use with water glass binders that water-repellent impregnation must be avoided in the mats.

An exemplary formulation of a molding composition for the production of exhaust manifolds with the thermal insulation layers described above is mentioned below:

1 part Si0 ₂ as a reference 1.4 to 2.7 parts H ₂ 0 0.25 to 0.5 parts Na ₂ 0 12 to 20 parts of corundum furnace filter dust, which together form the binder.

In addition there are 2 to 8 parts of reinforcing fibers and 0.5 parts of hollow glass spheres.

It is important that the binder, together with the reinforcing component, forms a sufficiently solid and quick-curing matrix that can withstand the sometimes violent shocks that occur in motor vehicles during normal operation.

The particulate pore-containing material mainly serves to improve the thermal insulation, and in many cases it may already be sufficient if the particulate, pore-containing material forms and keeps cavities in the matrix during the solidification and curing of the molding composition, while the fate of the Particulate, pore-shaped materials when using the thermal barrier coating as the outer layer of the exhaust manifold in the motor vehicle are of minor importance during the period of operation, due to the matrix, the cavities necessary for thermal insulation are also retained when the particulate, pore-containing material is in the course changes over time or will even burn out from the molded parts.

Fastening means which serve to fasten the exhaust manifold to the engine or to connect the exhaust manifold to the remaining parts of the exhaust system can be included or embedded in the thermal insulation layer. Such fastening parts can in particular be metal parts with an incorporated thread or with integrally molded flanges. The invention will now be explained in more detail with reference to the drawing. The individual shows:

1 shows a schematic illustration of an exhaust manifold according to the invention; and

FIG. 2 shows a sectional view through a thermal insulation layer of the exhaust manifold from FIG. 1 constructed according to the invention.

1 shows an exhaust manifold provided with the reference number 10, which comprises a branching or collecting pipe 12 and four connecting pipes 14 to 17. With the connection pipes 14 to 17, the exhaust manifold 10 can be connected directly to the matching internal combustion engine block or its exhaust outlets.

The illustration of the exhaust manifold according to the invention contained in FIG. 1 is a purely schematic illustration to explain the invention, and in particular the thicknesses of the individual component elements are selected only for the purposes of illustration. In particular, in the exhaust manifold according to the invention, the wall thickness of the header pipe 12 and the connecting pipes 14 to 17 is chosen to be very small in order to keep the heat capacity of these pipes as low as possible. The material from which these tubes are usually made is steel sheet, which can be shaped into the desired shape in one deformation step.

The exhaust manifold according to the invention further comprises a thermal insulation layer 18 which is placed around the manifold 12 and the connecting pipes 14 to 17. In the case of the embodiment shown in FIG. 1, the exhaust manifold 10 comprises two half-shells 20 and 21, which form the thermal insulation layer 18 around the collecting and connecting pipes.

It is particularly advantageous in this embodiment that, in the event of a repair, the thermal insulation layer 18, here in the form of the half-shells 20 and 21, can be removed from the header pipe or the connecting pipes and can thus be reused when the header pipe is replaced.

As mentioned above, in particular the thickness ratios of the thermal insulation layer 18 and the layer thickness of the header and connecting pipes are not drawn to scale, but are chosen only for the sake of simplicity of illustration.

Fig. 2 shows a sectional view through the structure of the heat insulation layer 18, which in this embodiment consists of a fiber mat 22 which is temperature-resistant up to about 800 to 1000 ° C and consists essentially of mineral wool or silicate wool, which briefly in a very liquid formulation for the molding compound was dipped.

Alternatively, the binder could be applied on one or both sides in a viscous formulation.

The wet fiber mat 22 produced in this way was pressed into a desired contour with the aid of a mold, that is to say wrapped around the metallic collecting pipe 12 with the connecting pipes 14 to 17. Since the mat is very flexible due to the impregnation with the molding compound, the simplest shapes and the lowest pressures are sufficient for this. The ceramic binder hardens Ambient temperatures in a few minutes, the molded part can be separated along the dividing line and then removed from the mold.

In the thermal barrier coating shown in Fig. 2, a molding compound gradient was generated across the layer cross-section, i.e. the proportions of the molding compound in the total mass of the insulating layer are greater at the surface areas 24 and 25 of the insulating layer 18 than in the central region 26. This distribution of the molding compound over the cross-section of the insulating layer not only makes it possible to save one molding compound when producing the insulating layer, but also improves it on the one hand the thermal insulation properties and surprisingly also the acoustic insulation properties and of course results in a lower overall weight for the exhaust manifold 10.

In addition, if the molding material is used sparingly, this leads to an optically acceptable surface and to a very low absorption of water and oil by the exhaust manifold 10.

If necessary, the surface can be refined, for example to improve radiation shielding or to visually enhance the exhaust manifold. The advantages of the exhaust manifold according to the invention are first of all that the inside of the exhaust manifold can be made very thin-walled, which enables considerable weight savings and, in particular, savings in the thermal capacity of the component without the overall strength of the component being reduced or complicated Manufacturing process must be used.

In addition, the reduction in the heat capacity of the exhaust manifold enables the car to be started up much more quickly. Talysators of the exhaust system and prevents the catalytic converter from delivering sufficient heat to the catalytic converter during continuous operation of the engine with low consumption (for example when the engine is idling). The structure of the thermal barrier coating 18, as shown in FIG. 2, can of course also be used for other parts of the exhaust system, so as to achieve a further saving in heat capacity and heat radiation from the exhaust system.

Claims

PATENT CLAIMS

1. Exhaust manifold for an exhaust system of an internal combustion engine with a tube forming the inside of the manifold with at least one connecting piece for connection to at least one combustion chamber of the internal combustion engine and with a heat insulation layer arranged around the tube, characterized in that the heat ¬ medial layer is made of a very quickly curable molding compound, which comprises a high-temperature-resistant binder, a particulate component of a porous material and a fibrous or needle-shaped reinforcing component, and that the thermal barrier layer as such forms the outer surface of the exhaust manifold.

Exhaust manifold according to claim 1, characterized in that the binder comprises an inorganic reaction mixture forming a ceramic matrix.

Exhaust manifold according to claim 2, characterized in that the inorganic reaction mixture is self-curing, temperatures of up to 80 ° C being generated by an exothermic reaction.

4. Exhaust manifold according to claim 2, characterized in that the inorganic reaction mixture comprises water glass, KOH and furnace filter dust of the corundum production.

5. Exhaust manifold according to claim 4, characterized in that the water glass consists essentially of soda-water glass.

Exhaust manifold according to one of claims 1 to 5, characterized in that the particulate component made of pore-containing material comprises hollow glass spheres, expanded glass, Ver¬ miculite and / or pearlite.

Exhaust manifold according to one of claims 1 to 6, characterized in that its specific density is <2 g / cm ³ , preferably <1.5 g / cm ³ .

8. Exhaust manifold according to one of claims 1 to 7, characterized in that the reinforcing component comprises nadei-shaped wollastonite, glass fibers, mineral fibers, mineral wool and / or metal fibers.

Exhaust manifold according to claim 8, characterized in that the needles or fibers of the reinforcing component have a length in the range from approximately 50 to approximately 200 μm, in the case of glass and metal fibers to approximately 15 mm.

10. Exhaust manifold according to one of the preceding claims, characterized in that the molding composition further contains a filler.

11. Exhaust manifold according to claim 10, characterized in that the filler comprises talc, mica, lime and / or recycled thermal insulation material in powder form.

12. Exhaust manifold according to claim 10 or 11, characterized gekenn¬ characterized in that the grain size of the filler ranges from 0 to about 200 microns with a wide grain size distribution.

13. Exhaust manifold according to one of claims 1 to 12, characterized in that the molding composition comprises inorganic pigments, in particular based on metal oxides.

14. Exhaust manifold according to one of claims 1 to 13, characterized in that the viscosity of the molding compound is <150 Pas.

15. Exhaust manifold according to one of claims 1 to 14, da¬ characterized in that the heat insulation layer comprises the fa¬ ser- or needle-shaped reinforcing component as a high temperature resistant fiber mat, which with the very quickly curable molding compound was soaked and modeled before the molding compound hardened.

16. Exhaust manifold according to claim 15, characterized in that the regions near the surface of the exhaust manifold comprise a higher proportion of molding material than those located away from the surface.

17. Exhaust manifold according to one of claims 1 to 16, da¬ characterized in that the branch pipe is a Me¬ tallblechteil.

18. Exhaust manifold according to one of claims 1 to 16, characterized in that the branch pipe is a ceramic component.

19. Exhaust manifold according to one of claims 17 or 18, da¬ characterized in that the wall thickness of the branching pipe is <2 mm.

20. Exhaust manifold according to one of the preceding claims, characterized in that the fibrous reinforcing component is contained as a high-temperature-resistant fiber mat with a pore volume, the pore volume being at least partially filled with the molding composition.

21. Exhaust manifold according to claim 20, characterized in that the fiber mat is impregnated only on its outer layers, preferably with a layer thickness <2 mm.

22. Exhaust manifold according to claim 20 or 21, characterized gekenn¬ characterized in that the thickness of the fiber mat is about 5 to about 20 mm, preferably 6 to 15 mm.

23. Exhaust manifold according to one of claims 20 to 23, characterized by the fact that the grain size of the particle-shaped component of the molding composition is selected such that penetration of the particles into the surface layers of the fiber mat is possible.

24. Exhaust manifold according to one of claims 1 to 19, characterized by the fact that the molding composition contains the reinforcing fibers or needles essentially singly distributed and is foamed.

25. Exhaust manifold according to one of the preceding claims, characterized in that the heat insulation layer is formed in several parts and can be removed from the branch pipe.

26. Exhaust manifold according to claim 25, characterized in that the parts of the thermal barrier coating are preformed.

27. Exhaust manifold according to one of claims 1 to 24, da¬ characterized in that the heat insulation layer is molded onto the branch pipe.

28. Exhaust system for an internal combustion engine, comprising an exhaust manifold according to one of the preceding claims.

29. Exhaust system according to claim 28, characterized in that it contains further pipelines covered with a thermal insulation layer, which corresponds in structure to the thermal insulation layer according to one of claims 1 to 27.