Abstract:
A composite air intake manifold includes a header and runners having communicating passages. The composite intake manifold is fashioned from carbon fiber cloth which is preferably impregnated with resin and cured between a meltable core mold and a split outside mold. The carbon fiber cloth is oriented throughout the manifold to give the manifold maximum pressure resisting capability with minimum thickness and weight. Because virtually any shape may be adopted for the interior passages of the header and the runners, the interior passages of the header and runners may be shaped to enhance air flow through the manifold.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. provisional application 60/553,927 filed Mar. 17, 2004. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a lightweight, composite air intake manifold for internal combustion engines and a method for making it. 
     BACKGROUND OF THE INVENTION 
     A need exists for lightweight intake manifolds for internal combustion engines capable of withstanding significant internal pressures. Many prior art intake manifolds have been fashioned from cast aluminum which, for a typical four cylinder internal combustion engine, may weigh approximately 15 pounds and may act to heat the intake air charge, adversely affecting performance. Moreover, there is a need for internal combustion engine intake manifolds having internal passages shaped and sized for efficient air flow. What is needed is a lightweight, high strength, low thermal mass intake manifold having internal passage geometry adapted to facilitate air flow and a method for making such an intake manifold. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In an embodiment of the present invention the aforementioned need is addressed by providing a lightweight composite air intake manifold and a method for making such a manifold which allows the manifold designer to optimize the internal passage geometry for efficient air flow. A composite air intake manifold of the present invention includes a header and runners having communicating passages. The composite intake manifold is fashioned from resin impregnated carbon fiber cloth which is preferably impregnated and cured between a meltable core mold and a split outside mold. The carbon fiber cloth is oriented throughout the manifold to give the manifold maximum pressure resisting capability with minimum thickness and weight. Because virtually any shape may be adopted for the interior passages of the header and the runners, the interior passages of the header and runners may be shaped to enhance air flow through the manifold. 
     The method for making the present air intake manifold preferably employs at least two complementary outside mold portions having inside surfaces corresponding to the desired outside surface of the manifold and a core mold having an outside surface corresponding to the desired inside surfaces of the internal manifold passages. The outside mold is preferably made from a durable material for repeated use. The core mold is preferably made from a meltable material such as for example a wax composition that is substantially impermeable to a thermosetting resin. It is important that the core mold material have a melting point that is above the temperature at which the thermosetting resin selected for the manifold cures and that is also below the temperature at which the selected resin begins to degrade after it has been cured. 
     The manifold is laid up by first placing portions of structural fiber cloth around the core mold. A spray adhesive may be used to position fiber cloth portions upon the complex curved outer surfaces of the core mold. Any appropriate fabric, such as carbon fiber fabric, fiber glass fabric or even ceramic fiber fabric may be used. The outside molds are closed around the fabric covered core mold. After the lay-up is assembled, liquid resin is transferred into the dry structural fabric through holes or channels in at least one of the outer molds. A resin and core mold material combination is selected such that the resin can be cured at a temperature below the melting point of the core mold material. After the resin is cured, the manifold is heated until the core mold material melts and drains out. As stated above, a core mold material and resin combination is selected such that the core mold material may be melted away without degrading the cured resin. A solvent may be used to wash out any remaining core mold material. Fittings for interfacing with other engine components may then be added to the manifold using appropriate adhesives. Alternatively, the fittings may be molded into the manifold if geometry permits. The resulting manifold is very light, may have excellent internal geometry for conducting air flow and may be very strong for resisting high internal pressures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a composite intake manifold. 
         FIG. 1B  is a side view of a composite intake manifold 
         FIG. 2  is an exploded view the molds needed to lay-up a composite intake manifold body including two outer mold pieces and a core mold. 
         FIG. 3A  is an plan view of a first fabric portion used to cover a runner. 
         FIG. 3B  is an plan view of a second fabric portion used to cover the header. 
         FIG. 3C  is an plan view of a third fabric portion used to cover the header having edges for forming seams that are spaced away from the seams formed by the second fabric portion. 
         FIG. 3D  is an plan view of a fourth fabric portion used to cover the header having edges for forming seams that are spaced away from the seams formed by the second and third fabric portions. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings,  FIGS. 1A and 1B  illustrates a composite intake manifold  10 . The composite intake manifold  10  includes a manifold body  10 A which further includes a header  12  and, in this example, four runners  14 A,  14 B,  14 C and  14 D extending from the body of header  12 . Each of runners  14 A,  14 B,  14 C and  14 D provides an outlet port. Runners  14 A,  14 B,  14 C and  14 D are bonded to an aluminum outlet fitting  15 A for mating with the intake ports of the cylinders of an internal combustion engine  300  shown in  FIG. 1B . Header  12  includes an inlet opening  12 A around which is bonded an inlet fitting  12 B for mating with the outlet fitting of an air supply  200  shown in  FIG. 1B  or other source of air. A second aluminum fitting  12 C is also glued to header  12 . Header  12  and runners  14 A,  14 B,  14 C and  14 D of intake manifold body  10 A are integrally formed with resin impregnated high strength fabric. The method for fabricating intake manifold body  10 A will be described in greater detail below. As can be seen in  FIG. 2 , intake manifold body  10 A is relatively thin walled. Because intake manifold body  10 A is relatively thin walled and fabricated from a high strength lightweight composite material, intake manifold  10  with bonded aluminum fittings  12 B,  12 C and  15 A has a weight that is approximately 30% of the weight of a traditional cast aluminum intake manifold. Intake manifold body  10 A may also have internal passages which may be advantageously shaped to facilitate air flow. 
       FIG. 2  presents an exploded isometric view of outside molds  102  and  104  as well as core mold  110  for fashioning an intake manifold body  10 A. As can be seen in  FIG. 2 , lay-up  100  includes a first outside mold  102 , a second compatible outside mold  104  and a core mold  110 . First and second outside molds  102  and  104  fit together in a clam shell fashion. First and second outside molds  102  and  104  are fashioned from a durable, reusable material. First outside mold  102  includes a mold impression  102 A which is offset from the outside surface of core mold  110 . Similarly, second outside mold  104  includes a corresponding mold impression (not shown) which is offset from the opposite outside surface of core mold  110 . The impressions of outside molds  102  and  104  define a surface that is offset from the outside surface of core mold  110 . These impressions are suitable for forming the outside surface of manifold body  10 A. This degree of offset is generally related to the desired thickness of manifold body  10 A. Second outside mold  104  is shown in  FIG. 2  to include a resin inlet port for receiving resin and conveying it to the interior impressions of mated first and second outside molds  102  and  104 . Core mold  110  is preferably fashioned from an expendable wax material which will be described in greater detail below. Core mold  110  includes a header portion  112  for forming header the inside surfaces of header  12  and runner portions  114 A,  114 B,  114 C and  114 D for forming the inside surfaces of runners  14 A,  14 B,  14 C and  14 D. 
       FIGS. 3A–3D  illustrate first, second and third structural fabric portions  132 ,  134  and  136  for covering core mold  110 . First structural fabric portion  132  shown in  FIG. 3A  is tube shaped and has a weave pattern having fibers oriented approximately 45 degrees to its central axis. This weave pattern allows for easy diametrical adjustment as a first fabric portion is placed around one of runner portions  114 A,  114 B,  114 C and  114 D. Although only one first fabric portion  132  is shown in  FIG. 3A , at least four and more likely some multiple of four such first fabric portions will be used to cover of runner portions  114 A,  114 B,  114 C and  114 D. Second, third and fourth fabric portions  134 ,  136  and  138  shown in  FIGS. 3B–3D  are for covering header portion  112 . Second fabric portion  134  includes corresponding edge openings  134 A,  134 B,  134 C and  134 D for clearing runner portions  114 A,  114 B,  114 C and  114 D as second fabric portion  134  is wrapped around header portion  112  of core mold  102 . Similarly, third fabric portion  136  shown in  FIG. 3C  includes openings  136 A,  1136 B,  136 C and  136 D for receiving runner portions  114 A,  114 B,  114 C and  114 D. Fourth fabric portion  138  shown in  FIG. 3D  also has a series of openings  138 A,  138 B,  138 C and  1138 D for receiving runner portions  114 A,  114 B,  114 C and  114 D of core mold  110 . However, the openings in fabric portion  138  have been offset so that the edges of fabric portion  138  will join at a different location on core mold  110  thus forming a seam at a different location than that formed by third fabric portion  136 . With the use of such offset openings, seams may be placed in other locations around header portion  112  of core mold  110 . This layering of seams with areas of fabric having no seams increases the strength of the resulting manifold body  10 A. The fabric portions shown in  FIGS. 3A–3C  are intended to be merely examples of the types of structural fabric patterns used to lay-up manifold body  10 A. The fabric portions described above may be applied in multiple plies to achieve a required capability for withstanding internal pressure. 
     The structural fabric portions described above may, for example, be fashioned from an aramid fiber such as du Pont KEVLAR® fiber or may, for example, be fashioned from fiber glass, carbon fiber or even ceramic fiber for advantageous thermal properties. Multiple layers of first structural fabric portions  132  may be laid up on each runner portion of core mold  110  and multiple layers of second, third and fourth fabric portions  134 ,  136  and  138  or other structural fabric portions having various offset opening locations for staggering the locations of seams may be laid up around core mold  110 . The number and type of fabric portions would depend on the intended operating environment and conditions of manifold  10 . For example, a high pressure manifold would require a larger number of layers of structural fabric. Because temperatures in an engine compartment may often exceed 150° F., a resin may be selected which is capable of resisting relatively high temperatures above 150° F. In the alternative, pre-impregnated sheets of structural cloth may be used. The resin present in such pre-impregnated cloth should have a curing temperature below the melting temperature of the core mold material and a degradation temperature above the melting temperature of the core mold material. 
     The process of laying up manifold body  10 A can be understood by referring to  FIG. 2 .  FIG. 2  is a perspective view showing outside molds  102  and  104  and core mold  110  used for making an intake manifold body  10 A according to the method of this invention. To conduct the process for making manifold body  10 A, the following components are needed: (1) a first outside mold  102 , (2) a second complementary outside mold  104 , (2) a core mold  110  and (3) at least four fabric portions  132  and at least a combination of fabric portions including at least two of fabric portions  134 ,  136  and  138 . Fabric portions  132 ,  134 ,  136  and  138  may all be fashioned from a dry, unimpregnated structural fiber fabric. In the alternative, some or all of them may be fashioned from structural cloth which is pre-impregnated with resin. 
     The applicant has found that the best core mold material for both first core mold  110  is a wax composition that is formulated to melt at a temperature above 160° F. Those skilled in the art can formulate a wax having a desired melting point. A supplier of industrial waxes such as Calwax, Inc. of Irwindale, Calif. can easily supply a wax composition having a desired melting point. For example, a wax composition consisting of 40 parts Calwax 126™ wax, 60 parts Calwax 252B™ wax and 1 part Calwax 320™ wax obtained from Calwax, Inc. will melt above 160° F. Ceramic micro-spheres or some other similar material can be added to the core mold composition to reduce thermal expansion effects at the curing temperature of the resin, to reinforce the core material structurally and to even reduce the weight of the core material. The addition of ceramic micro-spheres also makes it possible to compose core mold materials having such favorable thermal expansion characteristics that parts with larger internal volumes can be produced while maintaining the overall shape of the part within exact tolerances. Such space filling materials would also decrease the amount of heat needed to melt a volume of core mold wax. It is generally advantageous to reduce the thermal expansion effects associated with the core mold material. 
     The process for making manifold body  10 A includes a lay-up process, a resin impregnation step, a curing step and a core mold drain step. The process laying up manifold body  10 A shown in  FIGS. 1A and 1B  includes the following steps: (1) Structural fabric portions  132 ,  134 ,  136  and  138  are laid up around core mold  110 . A spray adhesive may be used to force the structural fabric portions to adhere to the complex curved surfaces of core mold  110 . (2) Core mold  110  with laid up fabric is placed between outside molds  102  and  104  which are then clamped tightly together. (3) Low viscosity resin is introduced into a resin entry port  104 A in one of the outside molds. (4) In the case of a resin used in combination with carbon fiber fabric, a typical curing temperature would be about 130° F. An isothermal transfer process may be conducted where heated resin is transferred, via pressure or vacuum or a combination of pressure and vacuum, into a heated lay-up at the resin curing temperature. However, an isothermal transfer process must be conducted rapidly so that resin flows into the layers of the lay-up before it begins to harden. 
     After the resin is cured, outer molds  102  and  104  are separated from manifold body  10 A. At this point, the core mold material can be melted and drained from manifold body  10 A. This is accomplished by heating the manifold body to a temperature which is above the melting point of the core mold material but below the point at which the cured resin of manifold body  10 A will degrade. The preferred wax composition described above can be melted efficiently at approximately 250° F. which is well below the temperature at which many resin resins will degrade. The melted core mold material can be recovered for future use. Core mold material residue can also be washed out with a solvent that will dissolve the core mold material but that will not attack the resin or carbon fiber material of the composite. What remains is a is an unfinished manifold body  10 A having excess material. After appropriate trimming of the excess material from manifold body  10 A, aluminum fittings  12 B,  12 C and  15 A may be glued to manifold body  10 A using a high strength adhesive, suitable for the application, thus completing intake manifold  10 . 
     It is to be understood that while certain forms of this invention have been illustrated and described, it is not limited thereto, except in so far as such limitations are included in the following claims and allowable equivalents thereof.