Abstract:
An exhaust manifold ( 10 ) of the present invention comprises a liner ( 12 ) that includes inner surface ( 14 ) defining manifold passages and an outer surface ( 16 ). The exhaust manifold ( 10 ) includes a shell ( 18 ) of a homogeneous and continuous material disposed over the outer surface ( 16 ) of the liner ( 12 ). The shell ( 18 ) and liner ( 12 ) of the exhaust manifold ( 10 ) include first ( 60 ) and second ( 72 ) composition formed from ferrous and non-ferrous metal powders ( 62 ), ceramic powder ( 64 ), and a binder ( 74 ) added thereto to form the manifold ( 10 ). The invention discloses a method of making the exhaust manifold ( 80 ). Accordingly, the exhaust manifold ( 10 ) of the subject invention has a reduced weight and dissipates heat energy contained in the exhaust thereby increasing the efficiency of the catalytic converter ( 42 ).

Description:
The present application claims priority to U.S. Provisional Patent Application No. 60/335,995 filed on Nov. 15, 2001. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The subject invention relates to an injection molding exhaust manifold having a ceramic liner and method of making the same. 
   2. Description of the Prior Art 
   Generally, catalytic converters used in the automotive industry, are usually heated by the engine exhaust gases. It is critically important to minimize the amount of a residual heat of the exhaust gases of an internal combustion engine to provide for highly efficient and effective catalytic converter that may reduce the emission levels of the engine. 
   Numerous, techniques for insulating exhaust manifolds and for providing other means to speed up light off have been suggested and known in the automotive industry today. One of the techniques known is a cast iron molding, disclosed in the U.S. Pat. No. 5,018,661 to Cyb, that shows a cast manifold comprising first and second sections cast in place from a metal to form a housing of the manifold. Hence, cast molded exhaust manifolds are heavy and increase the overall weight of the vehicle. The U.S. Pat. No. 5,682,741 to Augustin et al. and U.S. Pat. No. 5,419,127 to Moore, III show a welded tubing exhaust manifolds that have less mass, but are complicated and expensive to manufacture. Additionally, a double-walled welded tubing exhaust manifolds have been suggested, with an air gap between the walls, as shown in the Moore Patent cited above. Hence, double-walled exhaust manifold may be not cost effective, they are still complex to manufacture. 
   The related art also provides for other examples of exhaust manifolds being cast molded from a liquid metal having ceramic particles for use on vehicles. One such example is shown in U.S. Pat. No. 5,223,213 to Kamimura et al. The Kamimura Patent discloses an exhaust manifold having ceramic particles integrally formed within the exhaust manifold. However, the liquid metal used for casting the exhaust manifold may include defects, which reduces the strength of the exhaust manifold. 
   The approaches disclosed in the prior art patents, cited above, are expensive and add weight. Injection molding is a preferred process for manufacturing complex shaped parts from metal and ceramic powders. One such method is shown in U.S. Pat. No. 6,056,915 to Behi et al. The Behi Patent discloses method of making tools from injection molding procedures and includes the steps of inserting a mold into an injection molding apparatus, injecting powder metal feedstock into the mold, debinding the part for forming a green body, and sintering the part to form a completed part. However, the Behi Patent does not allow for multiple components to be combined into a single unitary piece. 
   Although the prior art patents disclose different designs of exhaust manifolds and methods of making the same, one of the opportunities of continuous development and research is the area of a more advanced design of an exhaust manifold and process of making the same that may provide for additional weight reduction and dissipation of heat energy contained in the exhaust thereby increasing the efficiency of the catalytic converter, and reduction of the manufacturing cost of the catalytic converter since the size of the catalytic converter may be reduced with increased efficiency. Still another area of continuous development and research is the area of a manifold design that may eliminate seams on the outer shell wherein the liner or insert is encapsulated by the outer shell continuously extending about the liner. 
   BRIEF SUMMARY OF INVENTION 
   An exhaust manifold comprises a liner that includes inner surface defining manifold passages and an outer surface. The exhaust manifold includes a shell of a homogeneous and continuous material formed from a metal powder and a ceramic powder and disposed over the outer surface of the liner, which includes a second homogeneous and continuous material formed from a metal powder and a ceramic powder. The invention discloses a method of making the exhaust manifold that comprises the steps of forming the liner that includes inner surface defining manifold passages and the outer surface, molding the shell of homogeneous and continuous material completely encapsulating the outer surface of the liner. The method further included the step of adding a binder to the homogeneous and continuous material and pelletizing the homogeneous and continuous material to form a feedstock wherein the homogeneous material is extruded through the extruder to form the feedstock. 
   Accordingly, the exhaust manifold of the subject invention has a reduced weight and dissipates heat energy contained in the exhaust thereby increasing the efficiency of the catalytic converter. Additionally, the method of the present invention provides for seam-free outer shell of the manifold. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
       FIG. 1  is a perspective view of an exhaust manifold; 
       FIG. 2  is a perspective view of the exhaust manifold combined with a catalytic converter; 
       FIG. 3  is a perspective cut away view of the exhaust manifold; 
       FIG. 4  is a cross-sectional view of the exhaust manifold; and 
       FIG. 5  is a schematic view of a method of making the exhaust manifold. 
       FIG. 6  is a schematic view of a method of making the exhaust manifold. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the  FIGS. 1 through 5 , wherein like numerals indicate like or corresponding part throughout the several views, an exhaust manifold for an internal combustion engine, is generally shown at  10 . The exhaust manifold  10  comprises a liner  12  that includes inner surface  14  defining manifold passages and an outlet surface  16 . The exhaust manifold  10  includes a shell  18  of a homogeneous and continuous material disposed over the outer surface  16  of the liner  12 . 
   The exhaust manifold  10  includes a housing, generally indicated at  20 , defined by the shell  18  and the liner  12 . The housing  20  includes a central portion, generally indicated at  22 , having inlet  24  and outlet  26  ends and side walls  28 ,  30 . The inlet end  24  of the central portion  22  includes an inlet flange  32  extending therefrom for mounting the exhaust manifold  10  to a surface of an engine  34 . The inlet flange  32  includes at least one aperture  36  therewithin to receive a male connector  38  to engage the inlet flange  32  with the surface of the engine  34 . The outlet end  26  of the central portion  22  includes an outlet flange  40  extending therefrom for mounting the exhaust manifold  10  to a catalytic converter  42 . The outlet flange  40  includes at least one aperture  44  therewithin to receive the male connector  46  to engage the outlet flange  40  with the catalytic converter  42 . 
   The central portion  22  of the housing  20  includes at least one outlet portion  48  outwardly extending from the side walls  28 ,  30  to a distal end  50  terminating into a flange  52 , which includes at least one aperture  54  therewithin to receive the male connector  46  to engage the outlet portion  48  with the engine  34 . The distal end  50  of the outlet portion  48  includes a boss  56  extending outwardly therefrom wherein the boss  56  includes an aperture  58  to provide for additional connection of the exhaust manifold  10  within the engine  34 . 
   The shell  18  of the exhaust manifold  10  includes a first composition, generally indicated at  60 , of the aforementioned homogeneous and continuous material, which is formed from ferrous and non-ferrous metal powders  62  and a ceramic powder  64 . The ferrous and non-ferrous metal powders  62  include, but not limited to iron, brass, copper, aluminum, stainless steel, nickel, tungsten, titanium, tool steel, or mixture thereof, and the like. The ceramic powder  64  of the first composition  60  includes aluminum oxide (Al 2 O 3 ), zirconia, steatite, or mixture and alloys thereof, and the like. The first composition  60  includes a binder  74  added thereto to form the shell  18 . The binder  74  comprises water, an agar solution, and a gel strength-enhancing agent and may be added to the first composition  60  to increase the strength of molded manifold  10  and resist cracking upon removal of the manifold  10  from die. Preferably, the agar solution may include and not be limited to other polymers such as polypropylene, polyethylene, polystyrene, polyvinyl chloride, paraffin wax, polyethylene carbonate, polyethylene glycol, and the like. Preferably, biocides may be added to the first composition  60  to impede bacteria growth. As illustrated in  FIG. 4 , the first composition ( 76 ) of the shell ( 18 ) includes between 49% to 99% of the metal powder in relation to the ceramic powder and the binder. 
   The shell  18  is disposed continuously over and encapsulates the outer surface  16  of the liner  12  that comprises first  66  and second  68  halves defining passages, generally indicated at  70 , therebetween to allow a gas flow run through the exhaust manifold  10 . The liner  12  includes a second composition, generally indicated at  72 , i.e. second homogeneous and continuous material, formed from the ferrous and non-ferrous metal powders  62  and a ceramic powder  64 , and the binder  74  added thereto. In one embodiment of the present invention, the second composition  72  includes between 0.1% to 99.9% of the ceramic powder  64  in relation to the metal powder  62  and the binder  74 . In the alternative embodiment of the present invention, the second composition  72  may include 100% of the ceramic powder  64 . 
   The subject invention also includes a method of making the exhaust manifold, generally shown at  80  in FIG.  6 . The method  80  comprises the steps of forming the liner  12  and molding the shell  18  of a homogeneous and continuous material completely encapsulating the outer surface  16  of the liner  12 . 
   As alluded to above the method  80  of the present invention begins with mixing the metal  62  and ceramic  64  powders to form the first  60  and second  72  compositions. The first  60  and second  72  compositions include the binder  74  added thereto, respectively, to form a homogeneous material of the first  60  and second  72  compositions. 
   The following step of the method  80  further includes pelletizing  82  the homogeneous material of the first  60  and second  72  compositions, respectively, to form a feedstock  84  wherein the homogeneous material is extruded through a twin barrel screw type extruder or mixture  86  to form the respective feedstock  84  and processed into pellets  88  for use in injection molding apparatus  90 ,  92 . Based on the embodiments of the present invention, the first composition  60  may include between 0.1% to 99.9% of the metal powder  62  in relation to the ceramic powder  64 . In the alternative embodiment, the first composition  60  may include 100% of the metal powder  62 . The second composition  72  may include between 0.1% to 99.9% of the ceramic powder  64  in relation to the metal powder  62 . In the alternative embodiment, the second composition  72  may include 100% of the ceramic powder  64 . 
   As alluded to above the following step of the present method  80  includes forming  92  the liner  12  in two halves  66 ,  68  wherein the second composition  72  is injected into the injection molding apparatus  90  followed by the step of debinding  94  the halves  66 ,  68  of the liner  12  removed from the injection molding apparatus  90 . The step of debinding  94  the liner  12  includes heating the liner  12  at the temperature between about 1200 to 1500° C. to allow portions of the binder  74  to be evaporated slowly from the liner halves  66 ,  68 . After a predetermined period of time, the step of debinding  94  is followed by the step of sintering  96  the halves  66 ,  68  of the liner  12  together wherein the liner  12  is heated between about 1000 to 1650° C. Similar to the debinding  94 , the sintering  96  of the liner halves  66 ,  68  includes putting together the liner halves  66 ,  68  and placing them in an oven (not shown). The oven is set at a desired temperature to sinter the liner halves  66 ,  68  together. The temperature of the oven depends upon the mixture of the powders  62 ,  64 , which form the feedstock  84 . Alternatively, the debinding  94  may occur at room temperature depending upon the feedstock  84 . 
   The next step  98  of the present method  80  includes positioning the liner  12  in the mold  92  and injecting the first composition  60  continuously over the outer surface  16  of the liner  12  to form the manifold  10 . Preferably, the vertical mold is used to inject the first composition  60  over the liner  12 . The step of injecting  98  the first composition  60  is followed by debinding  100  the manifold  10  by heating the manifold  10  at the temperature between about 200 to 500° C. The debinding  100  of the manifold  10  is followed by sintering  102  the manifold  10  to heat the manifold  10  between about 1000 to 1500° C. 
   Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims, wherein that which is prior art is antecedent to the novelty set forth in the “characterized by” clause. The novelty is meant to be particularly and distinctly recited in the “characterized by” clause whereas the antecedent recitations merely set forth the old and well-known combination in which the invention resides. These antecedent recitations should be interpreted to cover any combination in which the incentive novelty exercises its utility. In addition, the reference numerals in the claims are merely for convenience and are not to be read in any way as limiting.