Low thermal inertia integrated exhaust manifold

Abstract: A non-metallic vehicle gas-directing component (10) includes a plurality of ceramic members (36) embedded within an inner surface. The ceramic members (36) extend into a passageway (34) to form a boundary layer between the flow of exhaust gas and exposed portions of the inner surface (32) to provide a highly heat resistant and lightweight passageway for directing a high temperature gas. A method for producing the vehicle gas-directing component includes temporarily attaching a plurality of ceramic members to an inner mold core during a lost core molding process. In one disclosed embodiment, the ceramic members are temporarily attached directly to the inner mold core by an adhesive. In another disclosed embodiment, the plurality of ceramic members are attached to an inner contour of a core casting cavity by an adhesive.

Description: FIELD OF THE INVENTION The present invention relates to a vehicle gas-directing component, and more particularly to a non-metallic exhaust manifold with an inner surface having a plurality of embedded ceramic members. BACKGROUND OF THE INVENTION Various types of exhaust manifolds have been used in the field of internal combustion engines. Known exhaust manifolds are typically manufactured of a heat resistance metal such as cast iron to resist the high temperature exhaust gas emitted from the vehicle engine. However, these known manifolds are relatively heavy and tend to absorb much of the thermal energy generated by the exhaust gases. In order to reduce their weight, some known exhaust manifolds are constructed of a light metal such as aluminum. When using such a material for an exhaust manifold, it becomes necessary to line or coat the inner surface with a heat insulating material such as a ceramic. In one known exhaust manifold, a ceramic fiber layer coats the inner surface of the aluminum exhaust manifold. However, because of the great difference in the thermal expansion properties of metals and ceramics, prolonged use tends to induce undesirable separation of the ceramic layer from the metallic surface. Separation of the ceramic fiber layer typically results in the destruction of the light metal surface by the high temperature exhaust gas. Known iron exhaust manifolds have a high thermal conductivity and tend to immediately absorb much of the thermal energy generated by the exhaust gases. High thermal conductivity can be a disadvantage as the exhaust system catalyst can not immediately "light off" and a high percentage of total emissions occur before the catalysts are active. It would therefore be further desirable to prevent the exhaust manifold from manifold from absorbing the heat of the exhaust gases and allow the residual heat to activate the downstream catalytic converter. The catalytic converter will then "light off" earlier and will operate with higher efficiency which may effectively reduce the emission levels of the engine. Accordingly, it is desirable to provide a lightweight vehicle gas-directing component which can resist the highly heated exhaust gas emitted from the vehicle engine. US-A-5,888,641 (Atmur et al) provides a fibre reinforced ceramic matrix composite internal combustion engine exhaust manifold. US-A-5,052,513 (Showa & Yamamoto) provides a visco-elastic resin exhaust; WO 89/04915 (Showa & Yamamoto) provides a resin exhaust with cooling fins. US-A-5,404,721 (Ford Motor Company) teaches of a cast metal exhaust manifold having ceramic inner wall members. SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a method of forming a molded vehicle gas directing component comprising the steps: attaching a plurality of ceramic members to an inner mold core characterised in that the method further encompasses the steps; overmolding said inner mold core with a substantially plastic material to form a substantially plastics component; and removing said inner mold core such that said ceramic members are embedded in an inner surface of said plastics component. In accordance with a further aspect of the present invention there is provided a vehicle gas directing component comprising a substantially non-metallic duct for directing a gas, said duct having an inner surface characterised in that there are a plurality of ceramic members comprising spherical/granular/cubic/elliptical/rectangular shapes embedded in said inner surface, and in that an outer surface comprises a material such as nylon, PET, LCP, PP, PBT or various other plastics. The present invention thus provides a non-metallic vehicle gas-directing component having a plurality of ceramic members embedded within an inner surface and a method for producing the same. The inner surface preferably defines an exhaust passageway within an exhaust manifold for directing exhaust gas away from a vehicle engine. The ceramic members are embedded within the inner surface to be in direct contact with the exhaust gas. Notably, the ceramic members need not form a completely continuous layer along the inner surface. Because the ceramic members extend into the exhaust passageway, a boundary layer is formed between the flow of exhaust gas and exposed portions of the inner surface. Exhaust gases, although impacting the ceramic members, will tend to flow over the exposed inner surface portions because of the boundary layer. The method for producing a vehicle gas-directing component preferably includes temporarily attaching a plurality of ceramic members to an inner mold core during a lost core molding process. In one disclosed embodiment, the ceramic members are temporarily attached directly to the inner mold core by an adhesive. In another disclosed embodiment, the plurality of ceramic members are attached to an inner contour of a core casting cavity by an adhesive. By temporarily tacking the ceramic members to the inner contour, the ceramic members will be transferred to the outer contour of the inner mold core. The next step includes placing the inner mold core having the ceramic members attached to its outer contour within an outer core casting cavity and overmolding a non-metallic material over the surface of the inner mold core. The outer mold is sealed and the non-metallic material for forming finished component is injected or otherwise filled in between the inner mold core and outer core casting cavity of the outer mold. During the setting of non-metallic material, the ceramic members become embedded within what will become the inner surface of the finished component. After the non-metallic material is set within the outer core casting cavity, the finished component is removed and the inner mold core is destructively removed leaving the ceramic members embedded in the inner surface of the finished component. The inner surface of the finished component now includes the plurality of embedded ceramic members to provide, for example, a highly heat resistant and lightweight exhaust passageway for directing the exhaust gas as described above. BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: Figure 1 is a general perspective view of a vehicle exhaust system having an exhaust manifold designed according to the present invention; Figure 2 is an expanded view of the exhaust manifold of Figure 1; Figure 3 is a sectional view of the exhaust manifold of Figure 2 taken along the line 3-3; Figure 4A is an enlarged partially fragmented sectional view of a ceramic member according to the present invention; Figure 4B is an enlarged partially fragmented sectional view of a ceramic member according to the present invention; Figure 5 is a sectional view of the exhaust manifold of Figure 2 taken along the line 5-5 in Figure 2; Figure 6A is a schematic illustration of a step of the method of manufacture of the present invention; Figure 6B is a schematic illustration of a step of the method of manufacture of the present invention; Figure 6AA is a schematic illustration of an alternate step that replaces the steps illustrated in Figure 6A and 6B; Figure 6C is a schematic illustration of a step of the method of manufacture of the present invention; Figure 6D is a schematic illustration of a step of the method of manufacture of the present invention; Figure 6E is an expanded view of the finished component manufactured in accordance with the present invention; and Figure 7 is a flow diagram showing the steps of an embodiment of the process of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 illustrates a vehicle gas directing component 10 such as an exhaust manifold 10 affixed to an engine 12 and exemplary exhaust system 14. The exhaust system 14 typically includes an exhaust pipe 16, a connecting pipe 18, a catalytic converter 20, a straight pipe 22, a muffler 24, a second connecting pipe 26 and a tail pipe 28. In general, the engine 12 produces exhaust gas from the cylinders (not shown) which exit through the exhaust manifold 10. The exhaust gas, as schematically illustrated by the directional arrows E, passes through the exhaust manifold 10, through the exhaust pipe 16, connecting pipe 18 and the catalytic converter 20. The exhaust gas E continues through the catalytic converter 20, to the straight pipe 22, through the muffler 24, the second connecting pipe 26 and out into the atmosphere through the tail pipe 28. Referring to Figure 2, the exhaust manifold 10 includes inlet flanges 11 and an outlet flange 13. In use, the inlet flanges 11 are attached to the exterior of the engine block to mount the manifold thereon and the outlet flange 13 is attached to the exhaust system (Figure 1). Referring to Figure 3, a sectional view of the manifold 10 is illustrated. The manifold 10 has an outer surface 30 and an inner surface 32. The outer surface 30 is preferably manufactured of a non-metallic material such as nylon, PET, LCP, PPC, PBT or various other plastics. The inner surface 32 defines an exhaust passageway 34 for directing the exhaust gas away from the engine 12 (Figure 1). The inner surface 32 preferably includes a plurality of embedded ceramic members 36. The ceramic members 36 are positioned at least partially within the inner surface 32. The ceramic members 36 are preferably cast in place, as will be discussed in further detail below with respect to the method of manufacture of the present invention, such that the inner surface 32 is substantially coated with the ceramic members 36. Referring to Figure 4A, one disclosed embodiment provides a plurality of hollow ceramic spheres 38. A preferred hollow ceramic sphere 38 has an outer surface 39, and an inner surface 41 which defines the shape of an inner cavity 43. The preferred hollow ceramic sphere 38 has an outer diameter between approximately 19 to 25mm (0.75 to approximately 1 inch). The inner cavity 43 may be filled with a gas, for example air, or may be substantially devoid of gas, as in a vacuum. Referring to Figure 4B, another disclosed embodiment provides a ceramic sphere 38' having a plurality of grooves 45. The grooves 45 assist in the retention of the ceramic spheres 38' within the inner surface 32. Although, the grooves 45 are illustrated in a substantial checkerboard pattern, it should be realized that other groove orientations are contemplated. It is contemplated that the manifold 10 may have ceramic members 36 embedded therein which are not spherical in shape and are not of a consistent shape or size. For example only, granular, cubic, elliptical, and rectangular shaped ceramic members are also within the scope of the present invention, as is any shape that is amenable to disposition on the inner surface 32. Referring to the sectional view of Figure 5, the ceramic members 36 are embedded within the inner surface 32 of the manifold 10 in direct contact with the exhaust gas E from the engine 12. Notably, the ceramic members 36 need not form a completely continuous layer along the inner surface 32. As illustrated, inner surface portions 32' are exposed through the layer of ceramic members 36. Preferably the ceramic members 36 are arranged in relation to the direction of the exhaust gas E. Because the ceramic members 36 extend into the exhaust passageway 34, a boundary layer B is formed between the flow of exhaust gas E and the exposed inner surface portions 32'. The exhaust gas E, although impacting the ceramic members 36, tends to flow over the exposed surface portions 32' because of the boundary layer B. The exposed inner surface portions 32' are thereby not directly impacted by the exhaust gas E and the resulting high temperatures. The allowable size and spacing of the ceramic members 36, and the allowable size, spacing, and temperature exposure of the exposed inner surface portions 32' in part depends on the boundary layer. Calculation of these parameters is commonly determinable in the art of fluid dynamics and such calculations will not be further detailed herein. The ceramic members 36, the inner surface 32 and the outer surface 30, have different thermal expansion coefficients and encounter different temperatures. The surfaces will therefore expand and contract relative to each other. The substantially non-continuous layer of ceramic members 36 allows for this differential mechanical and thermal expansion. Thus, the probability of fracture over an extended time period commonly associated with continuous layers of ceramic material affixed to materials of differing thermal and mechanical expansion is reduced. Each ceramic member is of such a small dimension that the difference between its cold site and its hot site is a small amount. The plastics will easily accommodate this amount. A method for producing the above mentioned exhaust manifold will now be described. However, it should be realized that the use of an exhaust manifold is for illustrative purposes only, and that the methodology of the present invention may be applied to any other gas ducting vehicle components. Referring to Figure 6A, the first step (step 100 of Figure 7) is the forming of a first inner mold core 40 having an outer contour 42. The outer contour 42 produces the desired inner surface 32 of the finished component 10 such as the above described exhaust passageway 34 (Figure 2). The inner mold core 40 may be manufactured by any known method, such as the disclosed casting. The core casting cavity 44 includes an inner contour 46 which forms the outer contour 42 of the inner mold core 40. Preferable examples of the material for the inner mold core 40 include metallic materials having a melting temperature below that of the finished component material 10, such as Tin-Bismuth alloy. The next step (step 104, of Figure 7) includes temporarily attaching the plurality of ceramic members 36 to the inner mold core 40. The ceramic members 36 may be attached to the entire outer contour 42 or to selected locations of the finished component 10 which will be exposed to high temperatures. In one disclosed embodiment, the ceramic members 36 are temporarily attached directly to the inner mold core 40 by a simple adhesive. Preferably, the adhesive is non-toxic. Alternatively, referring to Figure 6AA another disclosed embodiment (steps 102a-102b, of Figure 7) includes temporarily attaching the plurality of ceramic members 36 to an inner contour 46' of the core casting cavity 44' by an adhesive. The adhesive preferably only lightly tacks the ceramic members 36 to the inner contour 46'. Again, the ceramic members 36 may be attached to the inner contour 46' of the core casting cavity 44' or to selected locations which correspond to desired locations on the finished component 10. By lightly tacking the ceramic members 36 to the inner contour 46' the ceramic members will be transferred to the outer contour 42' of the inner mold core 40'. Referring to Figure 6C, the next step (step 104, of Figure 7) is the step of overmolding a non-metallic material (shown schematically at 48) over the surface of the inner mold core 40 in a known manner. The inner mold core 40 having the ceramic members 36 attached to its outer contour 42 is placed in position within an outer mold 50 having a outer core casting cavity 52 which receives the non-metallic material 48 to form the outer surface 30 of the finished component 10. Outer mold 50 is sealed and the non-metallic material 48 for forming finished component 10 is injected or otherwise filled in between the inner mold core 40 and outer core casting cavity 52 of the outer mold 50. The non-metallic material used in this step is not particularly limited, and various plastics as described above, may be used singly or in combination. The inner mold core 40 having the ceramic members 36 attached to its outer contour 42 is now surrounded by the molten non-metallic material 48 within the outer core casting cavity 50. During the setting of non-metallic material 48, the ceramic members 36 become embedded within what will become the inner surface 32 of the finished component 10. Although a single non-metallic material is molded over the inner mold core 40 in a single step in the illustrated embodiment, two or more different non-metallic materials may be molded in additional steps over the inner mold core 40 until the desired outer surface 32 is formed. Referring to Figure 6D, the outer core casting cavity 50 is separated after the non-metallic material 48 has set. The outer surface 32 of the finished component 10 is now substantially complete while the inner mold core 40 remains within the finished component 10. Unnecessary portions of the outer surface may now need to be cut away in a known manner to obtain the desired finished component 10 outer surface 32 contours. Referring to Figure 6E, the inner mold core 40 is now destructively removed leaving the ceramic members 36 embedded in the inner surface 30 of the finished component 10 (Step 108 of Figure 7). Preferably, the inner mold core 40 is removed by melting as known in a variety of lost core molding processes. Because the inner mold core 40 has a melting temperature below that of the set non-metallic material, the finished component 10 is unaffected. The inner surface 32 now includes the plurality of embedded ceramic members 36 to provide a highly heat resistant and lightweight exhaust passageway 34 for directing the exhaust gas as described above. The basic molding techniques discussed above may rely upon steps and parameters as known in the basic art of lost core molding. It is the inclusion of the ceramic particles into the inner core which is inventive here. The foregoing description is exemplary rather than limiting in nature. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are possible.

Claims: A method of forming a molded vehicle gas directing component (10) comprising the step of: (a) attaching a plurality of ceramic members to an inner mold core (40); characterised in that the method further comprises the steps; (b) overmolding said inner mold core with a substantially plastics material to form a substantially plastic component; and (c) removing said inner mold core such that said ceramic members are embedded in an inner surface of said plastics component. A method according to claim 1, wherein said step (a) includes attaching said plurality of ceramic members to said inner mold core by an adhesive substance. A method according to claim 1, wherein said step (a) includes: (aa) attaching said plurality of ceramic members to an inner surface of a core casting cavity; (ab) casting said inner mold core within said core casting cavity; and (ac) removing said core casting cavity such that said ceramic members are attached to said inner mold core. A method as recited in claim 3, wherein said step (aa) includes attaching said plurality of ceramic members to said core casting cavity by an adhesive. A method as recited in claim 1, wherein said step (c) includes melting said inner mold core. A method as recited in claim 1, wherein said step (a) includes casting said inner mold core of a substantially tin-bismuth material. A vehicle gas directing component comprising a substantially non-metallic duct for directing a gas (10), said duct having an inner surface (32); characterised in that there are a plurality of ceramic members (36) comprising spherical/granular/cubic/elliptical/rectangular shapes embedded in said inner surface, and in that an outer surface (30) comprises a material such as nylon, PET, LCP, PP, PBT or various other plastics. The component according to claim 2, wherein said ceramic members are hollow ceramic spheres. The component according to claims 7 or 8, wherein said ceramic members are of a substantially uniform diameter within a range from 18 to 25mm. The component according to any one of claims 7 to 9, wherein said ceramic members form a substantially non-continuous layer, partially embedded within said inner surface. The component as recited in claim 9, wherein said ceramic members are arranged along said inner surface in relation to a flow direction of said\gas to form a boundary layer between said gas and said inner surface exposed through said substantially non-continuous layer. The component according to any one of claims 7 to 10, wherein said ceramic members include a plurality of grooves. The component according to any one of claims 7 to 12, wherein said component is an exhaust manifold.

Inventors: DALY PAUL D, DALY, PAUL D.
Applicants: SIEMENS VDO AUTOMOTIVE CORP, SIEMENS VDO AUTOMOTIVE CORPORATION
Application year: 2000
Main classification: F01N7
IPC codes: F01N7