Abstract:
An air duct is constructed with a rolling annular portion that is desirably formed of a series of hemi-toroid planar-cut surfaces. The rolling annular portion may include an inner portion and an outer portion constructed of different materials. The rolling annular portion permits relative movement within the air duct while minimizing disturbances in airflow.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to air ducts interconnecting components that may experience relative movement and in particular to air ducts with improved airflow characteristics.  
       BACKGROUND OF THE INVENTION  
       [0002]     Air ducts are provided in internal combustion engine applications as a means to channel airflow from one component to another. A typical application is an elongated air duct that channels filtered air from the outlet of an air filter housing to the engine intake. To prevent the introduction of contamination into the engine, the air duct is sealed to both the air filter housing and the engine intake. Often, the engine air filter housing is not mounted directly to the engine and, therefore, the air filter housing and the engine experience relative movement therebetween during engine operation. To accommodate this relative movement without compromising the air duct seals, the air may incorporate a flexible region, as described below.  
         [0003]     Referring to  FIGS. 1-3 , a prior art air duct  20  is illustrated. Air duct  20  includes an elongate hollow body  22  defined by an inlet opening  24 , an outlet opening  26 , and a undulating region  28 . The undulating region  28  is located within body  22  and includes hemi-toroid portions  30  extending therefrom. As illustrated, inlet opening  24  is larger than outlet opening  26 .  
         [0004]     As best seen in  FIG. 2 , hemi-toroid portions  30  are typically defined by an inside surface  32  and an outside surface  34 . Each of the inside surface  32  and the outside surface  34  define a shape that closely resembles a series of concave and convex surfaces. Hemi-toroid portions  30  are hemi-toroid in shape with each hemi-toroid portion  30  sectioned from a true torus by a cylindrical cut.  
         [0005]     Undulating region  28 , if not all of air duct  20 , is typically constructed of a flexible material. Undulating region  28  provides a desired amount of flexibility within air duct  20  to allow inlet opening  24  and outlet opening  26  to move independently. Generally, undulating region  28  permits about 2 inches of relative movement between inlet opening  24  and outlet opening  26 . Also, undulating region  28  allows installation of air duct  20  after the air filter housing and engine intake are secured, and accommodates a limited amount of mis-alignment.  
         [0006]      FIG. 3  illustrates relative positions of air duct  20  in section as undulating region  28  accommodates relative movement between inlet opening  24  and outlet opening  26 . As outlet opening  26  is deflected to the position of outlet opening  26 ′, elongate body  22  is distorted to the outline  22 ′ and undulating region  28  is distorted to the outline  28 ′. This distortion within air duct  20  causes airflow A to be deflected as generally represented by a non-linear path N.  
         [0007]     One disadvantage of the undulating region  28  is that as the air duct  20  accommodates relative movement between inlet opening  24  and outlet opening  26 , the elongate body  22  is distorted such that air flow A through air duct  20  follows the non-linear path N ( FIG. 3 ). This non-linear path N restricts the airflow A within air duct  20 .  
         [0008]     Another disadvantage of an undulating region  28  is the undesirable disturbance in airflow A ( FIG. 2 ) through air duct  20 . As air flows through air duct  20  from inlet opening  24  to outlet opening  26 , a smooth, laminar airflow is desired through air duct  20 . However, undulating region  28  introduces a turbulent air flow T. Turbulent airflow T is partly due to the non-uniform inside surface  32  and the pressure drop within air duct  20  associated with the increase in area provided by undulating region  28 . What is needed, therefore, is an air duct with a flexible region that will desirably accommodate relative movement between the openings of an air duct, while minimizing any disturbances in air flow.  
       SUMMARY OF THE INVENTION  
       [0009]     An embodiment of the present invention provides an air duct having an elongate body that includes a first opening, a second opening and a displacement portion. The displacement portion selectively accommodates an axial displacement within the elongate body between the first opening and the second opening. The displacement portion includes a rolling annular portion. The elongate body is adapted to minimize disturbances in airflow.  
         [0010]     Another embodiment of the present invention provides a rolling annular portion for an air duct. The rolling annular portion includes an inner portion having an outer periphery and an outer portion. The outer portion is positioned about at least a portion of the outer periphery of the inner portion. The outer portion and the inner portion are formed of different materials. At least a portion of the outer periphery is selectively formed into at least one planar-cut hemi-toroid surface.  
         [0011]     Yet another embodiment of the present invention provides a method of manufacturing an air duct. The method includes forming a first material in a mold to produce a first portion of the air duct, and forming a rolling annular portion in a desired region of the air duct. The rolling annular portion is selectively adapted to minimize disturbances in airflow. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0013]      FIG. 1  is a perspective view of a prior art air duct.  
         [0014]      FIG. 2  is a partial sectional view of the air duct of  FIG. 1 .  
         [0015]      FIG. 3  is a sectional view of the prior art air duct of  FIG. 1 , illustrated in a distorted shape.  
         [0016]      FIG. 4  is a perspective view of an air duct in accordance with an embodiment of the present invention.  
         [0017]      FIG. 5  is a partial sectional view of the air duct of  FIG. 4 .  
         [0018]      FIG. 6  is similar to  FIG. 5 , showing the air duct in an extended position.  
         [0019]      FIG. 7  is similar to  FIG. 5 , showing the air duct in a retracted position.  
         [0020]      FIG. 8  is a flowchart illustrating an embodiment of a method for producing an air duct in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0021]     Referring to  FIGS. 4 and 5 , an embodiment of an air duct  40  is illustrated. Air duct  40  includes an elongate hollow body  42  defining an inlet opening  44 , an outlet opening  46 , and an undulating region  48 . Undulating region  48  is located within body  42  and includes hemi-toroid portions  50  formed therein. Each hemi-toroid portion  50  includes a concave surface  52  and a convex surface  54 . Air duct  40  has a generally constant wall thickness T throughout. Stiffening members  56  are attached to body  42  in desired regions.  
         [0022]     Hemi-toroid portions  50  are curved, annular regions of air duct  40  with each hemi-toroid portion  50  sectioned from a hollow torus (not shown) by a plane that, in the embodiment shown, bisects the torus. Thus, hemi-toroid portions  50  can also be referred to as planar-cut hemi-toroid portions  50 .  
         [0023]     As best illustrated in  FIG. 5 , undulating region  48  includes a series of hemi-toroid portions  50  whose concave surfaces  52  face opposing directions, and form opposing planar-cut hemi-toroid surfaces. In contrast,  FIGS. 1-3  illustrate that prior art undulating region  28  includes a series of hemi-toroid portions  30  whose concave surfaces face opposing directions, yet this configuration forms opposing cylindrical-cut hemi-toroid surfaces.  
         [0024]     With reference to  FIGS. 5-7 , outlet opening  46  generally defines a plane S, indicated by line S-S. A plane R intersects elongate body  42  in the same location of air duct  40  in each of  FIGS. 5-7 . Outlet opening  46  also has an axis B-B that is generally normal to plane S. In the configuration illustrated in  FIG. 5  axis B-B is normal to plane R. Airflow A travels generally parallel to axis B-B when exiting outlet opening  46 . Generally, the region of air duct  40  that is located between planes R and S is a flexible portion  60 .  
         [0025]     Air duct  40  has an inner portion  62  having an outer periphery  64 , and an outer portion  66 . Inner portion  62  is constructed of at least a first material  72  and outer portion  66  is constructed of at least a second material  76 . Stiffening members  56  are also constructed of the second material  76 . Preferably, the outer portion  66  completely encases the outer periphery  64 . Also preferably, first material  72  is more flexible than second material  76 , as discussed in greater detail below. The region of air duct  40  exclusive of the flexible portion  60  is rigid portion  80 . Inner portion  62  has a thickness TI that varies within air duct  40 , and outer portion  66  has a thickness TO that varies within air duct  40 , as discussed in greater detail below.  
         [0026]     Thickness TI of inner portion  62  is preferably greater than thickness TO of outer portion  66  within flexible portion  60 . Thickness TO of outer portion  66  is preferably greater than thickness TI of inner portion  62  within rigid portion  80 . In the embodiment illustrated, thickness TI is about 90% of thickness T within most of the flexible portion  60  and thickness TO is about 90% of thickness T within most of the rigid portion  80 . Since the first material  72  is more flexible than the second material  76 , the flexible portion  60  is more flexible than the rigid portion  80 .  
         [0027]     Thicknesses TI and TO vary in the region adjacent plane R as indicated by outer periphery  64  in  FIGS. 5-7 . While this variance in thicknesses has been illustrated in one possible configuration in  FIGS. 5-7 , the transition between flexible portion  60  and rigid portion  80  may be a gradual transition in thicknesses, or an abrupt change in thicknesses.  
         [0028]     Flexible portion  60  is moveable between an extended position ( FIG. 6 ), and a retracted position ( FIG. 7 ). Preferably, the distance between planes R and S in  FIG. 6  is more than 2 inches greater than the distance between planes R and S in  FIG.7 .  
         [0029]     As best seen in  FIGS. 5-7 , flexible portion  60  can accommodate some amount of angular misalignment between axis B-B and a line normal to plane R. Additionally, flexible portion  60  can accommodate some amount of displacement between axis B-B and a line normal to plane R.  
         [0030]     Rigid portion  80  resists distortion as flexible portion  60  accommodates displacement and/or rotation between inlet opening  44  and outlet opening  46 . While some distortion within rigid portion  80  may occur as flexible portion  60  accommodates displacement and/or rotation between inlet opening  44  and outlet opening  46 , the airflow characteristics of air duct  40  remain relatively unchanged. As discussed earlier, the prior art undulating region  28  may result in undesirable levels of distortion in air duct  20  that causes degradation of airflow characteristics ( FIG. 3 ).  
         [0031]     Preferably, flexible portion  60  does not elastically expand, but rather the hemi-toroid portions  50  roll as best seen when contrasting the relative positions of planes R and S in  FIGS. 5-7 . Therefore, undulating region  48  is referred to as a rolling annular portion.  FIG. 5  generally depicts undulating region  48  in a preferred as-formed state.  
         [0032]     Flexible portion  60  is defined by planar-cut hemi-toroid surfaces at least during portions of the axial displacement of outlet opening  46 , as represented in  FIGS. 5 and 7 . However, flexible portion  60  is not defined by planar-cut hemi-toroid surfaces when in the extended position of  FIG. 6 .  
         [0033]     Preferably, the first material  72  is Santoprene™ or other relatively flexible thermoplastics with favorable blow-molding characteristics. Also preferably, the second material  76  is polypropylene, or other relatively rigid thermoplastics with favorable blow-molding characteristics. While undulating region  48  has been described as including two planar-cut hemi-toroid portions  50 , undulating region  48  may include any number of planar-cut hemi-toroid portions  50 , or may include portions that deviate from an exact hemi-toroid shape.  
         [0034]      FIG. 8  illustrates one embodiment of manufacturing the air duct  40  using extrusion blow molding. In step  100 , the first material  72  and the second material  76  are co-extruded to form a parison (not shown). Thus formed, the parison is a generally hollow cylinder formed with the first material positioned within the second material  76 . The parison extrudes with a calibrated measure of pre-blow to prevent collapse.  
         [0035]     In step  110 , the parison is positioned within a mold. In step  120 , the mold is closed, pinching the axial end of the parison that is opposite the axial end connected to the blowing apparatus. In step  130 , air or other gas is introduced through the blowing apparatus and into the parison, inflating the parison to expand until the parison contacts the interior surfaces of the mold. In step  140 , the mold is opened, and the molded form is removed. In step  100 , the molded form is trimmed to produce an air duct  40 . The mold includes mold portions that are defined, at least in part, by the interior surfaces of the mold and a mold portion interface. Each mold portion interface includes at least one generally planar mold interface surface. The mold interface surfaces are in contact when the mold is closed.  
         [0036]     Preferably, the air duct  40  is interposed between a primary air filter housing (not shown) and an engine air intake. Even more preferably, the air duct  40  is interposed between a primary air filter housing (not shown) and a turbo charger air intake.  
         [0037]     While the invention has been described with respect to specific examples including preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.