TECHNICAL FIELD 
     This invention relates to air induction systems that deliver clean air to an engine&#39;s air intake manifold. 
     BACKGROUND 
     Internal combustion engines require an air intake or induction system for capturing, cleaning and directing air into the combustion chambers of the engine. Typically, such air induction systems have an air inlet tube attached to the front structure of a vehicle, for example, the front inner fender or behind the headlamps. The inlet tube has an open end for taking in outside air and an opposite end that is connected to an air filter box containing an air filter. The air filter box cleans the intake air by passing it through the filter. In addition, the air filter box provides broadband attenuation of the noise generated by the pressure differential across the inlet valve during the air induction event. The filtered air is then drawn through the air induction outlet tube, through the intake manifold, and into the engine. The clean air is mixed with fuel and the mixture is combusted in the combustion chambers of the engine. 
     One problem confronting air induction system designers is the noise created by the engine during the air induction event. The noise signature is defined, in part, by the creation of acoustic standing waves that resonate within the air induction system. Prior art induction system designs have tried to address this problem by changing the dimensions of the ducted system as well as including reactive silencers, porous ducts, tuning holes, expansion chambers, etc., within the air induction system. Another problem confronting prior art air induction systems is the collection of water, snow, heat, and debris into the system. Conventional air induction systems addressed this problem by locating the inlet in an environmentally low-risk area of the vehicle. However, while these prior art air inlet tube designs have addressed some of the issues described above, problems still exist. 
     Therefore, there is a need for an new and improved air induction system having components that address both the collection of water/snow/heat/debris and the noise problems prevalent in prior art systems. The new and improved air induction system will allow the components to be packaged in environments where prior art components couldn&#39;t be packaged. 
     SUMMARY 
     The present invention is generally directed to an air induction system for inducting air into an engine of an automobile. The air induction system includes an air cleaner, an air outlet tube, an air inlet tube and reactive silencers (e.g., Helmholtz resonators and ¼ wave tuners). The air induction system is in fluid communication with the engine of the automobile for filtering intake air inducted into the engine and attenuating the noise produced during the air induction event. The air inlet tube is made of a first material and connected at a first end to the air cleaner and open to ambient air at a second end. The inlet tube has a flexible portion made of a second material that flexes as a result of internal pressure fluctuations during air induction into the engine. It is understood that the other components of the air induction system may incorporate the flexible portion without departing from the spirit of the invention. 
     In an aspect of the present invention, the flexible portion includes an aperture disposed along a length of the air induction system and covered with a second material. 
     In another aspect of the present invention, the second material of the air induction system is a thermoplastic elastomer and is made of an olefin/polypropylene blend. 
     In yet another aspect of the present invention, the air induction system has a flexible portion located substantially at a central portion of the air inlet tube. 
     In yet still another aspect of the present invention, the first material of the air intake tube is a polymer. 
     In yet another aspect of the present invention, the flexible portion of the air induction system has an aperture that is an elongated slot. 
     In still another aspect of the present invention, a method for reducing noise generated in an air induction system is provided. The method includes determining the dimensions of the air induction system, determining a location along the system where a maximum pressure of an acoustic standing wave(s) is present, forming a flexible portion into a portion of the air induction system, and positioning the flexible portion at the location of the maximum pressure of the acoustic standing wave. Thus, the method of the present invention provides an air induction system that flexes and reduces or eliminates noise generated by standing acoustic waves present in the system. 
     These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description of the invention in combination with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an engine and air induction system connected thereto of a vehicle, in accordance with an embodiment of the present invention; 
         FIG. 2  is a side view of the air inlet tube of the air induction system of the vehicle shown in  FIG. 1 , in accordance with an embodiment of the present invention; and 
         FIG. 3  is a side view of the opposite side of the air inlet tube shown in  FIG. 2 , in accordance with an embodiment of the present invention. 
     
    
    
     DESCRIPTION 
     Referring now to  FIG. 1 , a partial perspective view of a vehicle  10  having an air induction system (AIS)  12  is illustrated, in accordance with an embodiment of the present invention. Vehicle  10  is, generally, an automobile having an engine  14  such as an internal combustion engine which requires a supply of clean ambient air. As generally known, engine  14  mixes the fresh ambient air with an appropriate level of fuel. Engine  14  inducts the ambient air into the cylinders of the engine using AIS  12 . 
     AIS  12  includes an air induction manifold  16 , an air outlet duct  18 , a filter box  20 , and an air intake tube  22 . Air intake manifold  16  is of a conventional type that distributes intake air to the various engine cylinders where the air is mixed with a supply of fuel. The manifold  16  is connected to filter box  20  by air outlet duct  18 . Filter box  20  typically includes a filter (not shown) which traps debris carried in the ambient air, thereby supplying air manifold  16  with clean air. Air inlet tube  22  communicates ambient air from outside of the air intake manifold into air filter box  20 . 
     It should be understood that various aspects and features of the air induction system  12  may be changed without departing from the scope and spirit of the invention. For example, other air intake manifolds  16 , air outlet ducts  18 , and air filter boxes  20  may be utilized in combination with air inlet tube  22 . 
     Referring now to  FIG. 2 , a perspective view of a first side  21  of air inlet tube  22  is illustrated, in accordance with an aspect of the present invention. Air inlet tube  22  is generally an elongated tubular body connecting air filter box  20  to the ambient air. Depending on the particular vehicle packaging constraints, the tubular body of air inlet tube  22  may include various bends or tapers and the like to fit within the physical constraints of vehicle  10 . Generally, air inlet tube  22  is made of polypropylene or other suitable material blended with an additive such as a mineral filler (i.e. mica or talc) to increase the rigidity of the tube. 
     Air inlet tube  22 , in an embodiment of the present invention, includes a plurality of elongated apertures  26 . Elongated apertures  26  are formed in the tubular body of inlet tube  22  by various means including injection molding, milling or cutting and the like. The inlet tube is typically made of a thermoplastic material or other suitable polymer. Elongated apertures  26  are covered with a compliant member  28  to form a flexible portion or compliant member  28  of the air inlet tube. Compliant member  28 , in an embodiment of the present invention is a thermoplastic elastomer olefin blended with a polypropylene. For example, a material available and known as Santoprene™ may be used for this purpose. Santoprene™ is available through Advanced Elastomer Systems of Akron, Ohio. The present invention contemplates the use of other materials and other thermoplastic elastomers such as PVC, EPDM and the like. In still another embodiment of the present invention, compliant member  28  is a layer of a thermoplastic elastomer olefin blended with a polypropylene or other suitable material that is substantially thinner than the wall of the air intake tube. For example, compliant member  28  may be 0.5 to 1.5 millimeters thick, while the rest of the inlet tube  22  is between 2.0 and 3.0 millimeters thick. 
     Compliant member  28  is configured to undergo flexing relative to inlet tube  22  to reduce or eliminate the maximum pressure generated in the inlet tube by resonating standing waves. Typically, the standing wave, which is an acoustic wave, will be generated in a given length of inlet tube and will have a maximum pressure along discrete portions of the tube. As the pressure builds up through the formation of the standing wave, compliant member  28  flexes relative to the inlet tube  22  and reduces or eliminates the resonating acoustic wave. In this manner, the embodiments of the present invention significantly reduce or eliminate the noise generated by AIS  12 . While elongated apertures  26  and compliant material  28  are shown generally along a central portion of inlet tube  22 , the present invention contemplates other locations and positioning of the apertures and compliant material. For example, in other embodiments of the present invention, a single aperture covered with a compliant material may be used. On the other hand, in still other embodiments, two or more elongated apertures covered by compliant member  28  may be utilized. Inlet tube  22  may be formed by joining two elongated C-shaped (in cross-section) halves or by one unitary body. 
     In still other embodiments of the present invention, compliant member  28  may be located on other components of AIS  12 . For example, compliant member  28  may be disposed on air outlet tube  18  or air filter box  20 , as shown in  FIG. 1 . Furthermore, if AIS  12  has quarter wave tuners  17 , resonators  19  or the like, complaint member  28  may be disposed on these components as well, as illustrated in  FIG. 1 . 
     Referring now to  FIG. 3 , the opposite side  25  of inlet tube  22  is illustrated, in accordance with an embodiment of the present invention. As illustrated, side  25  of inlet tube  22  may have one or more elongated apertures  26 ′ as well. Apertures  26 ′ are covered with compliant material  28  as disclosed previously with regard to the side  21  of inlet tube  22 . Apertures and compliant covering  26 ′,  28  are positioned generally along a central portion of inlet tube  22 , however, the present invention contemplates other locations such as closer to either end of inlet tube  22 . Additional compliant portions  28  covering aperture  26 ′ allow for a further reduction in standing waves created in inlet tube  22 . Of course, suitable attachment features may be incorporated into or attached to inlet tube  22  to secure the inlet tube to the vehicle body. 
     In yet another embodiment of the present invention, a method for constructing air inlet tube  22  is provided. Before compliant member  28  is formed into the air intake tube a determination is made, based on the dimensions of the tube, as to where along the length of the tube the points or areas of maximum pressure exist from the creation of the acoustic standing wave(s). Once the maximum pressure points or areas are identified the air inlet tube may be constructed according to the following process, for example. In an initial step, air inlet tube  22  is formed by injection molding a first and second elongated half (the first half is shown in  FIG. 2  and the second half is shown in  FIG. 3 ). Of course, other molding processes may be utilized and are contemplated by the present invention. In a second step, compliant material  28  is over-molded over apertures  26  and  26 ′ that are disposed on the elongated apertures. The over molding process of the second step is a conventional process wherein the molded first and second halves are placed in a second mold and the compliant material is injection molded into the second mold. During the over-molding process, compliant member  28  fuses to the premolded air inlet tube halves and covers elongated apertures  26  and  26 ′. Of course, the present invention contemplates other methods for covering elongated apertures  26  and  26 ′ with compliant member  28 . For example, compliant material  28  may be heat staked or glued to the inner or outer surfaces of the inlet tube. 
     Thus, the present invention has many advantages and benefits over the prior art. For example, the air inlet tube of the present invention reduces or eliminates acoustic noise generated by standing waves resonating in the air inlet tube. A compliant material is provided in the inlet tube that is resistant to the harsh environments of an automobile and thus can be packaged in areas on the vehicle that were previously unavailable. Further, it follows from the description of the various embodiments of the present invention that the thickness of complaint member  28  should be decreased relative to thickness of the duct if more acoustic wave dissipation is required and increased if less acoustic wave dissipation is required. 
     As any person skilled in the art of air induction systems for engines will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims. It is further understood that other ducted-system applications requiring the dissipation of acoustic standing waves would also benefit from the incorporation of a properly located flexible membrane (i.e. compliant member  28 ).
An air induction system for inducting air into an engine of an automobile is disclosed. The air induction system has an air cleaner and an air inlet tube. The air cleaner is in fluid communication with the engine of the automobile for filtering intake air inducted into the engine. The air inlet tube is made of a first material and is connected at a first end to the air cleaner and open to ambient air at a second end. The inlet tube has a flexible portion that flexes as a result of internal pressure pulsations during the air induction event. The flexing reduces or eliminates acoustic standing waves that have significant pressure fluctuations at the same location in the air induction system as the flexible portion.