Abstract:
A heating, ventilation, and air conditioning (HVAC) case and duct for passively reducing noise, vibration and harshness (NVH) during operation of the HVAC system. The duct includes an outer wall defining a inner chamber opening into, for example, a passenger compartment of a motor vehicle. Interior walls define at least first and second air passages. A first air stream flows through the first air passage to the ventilation port. The second air passage intersects the first air passage upstream of the ventilation port at an output aperture. The second air stream may flow into the first air passage through the output aperture including a slotted wall to reduce NVH.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to heating, ventilation, and air conditioning (HVAC) systems. More specifically, the invention relates to a duct for use in a motor vehicle HVAC system having passive noise reduction. 
         [0003]    2. Description of Related Art 
         [0004]    In existing HVAC systems, ducts are used to direct air to desired locations. The ducts often contain various elements that can be a significant source of noise, vibration and harshness (NVH) when the HVAC system is in operation. The noise is particularly evident where two air streams mix within the ducts. For example, hot air downstream of a heater core generally has higher pressure than cool air downstream of, for example, a condenser. Therefore, when a hot air stream and a cold air stream mix, there can be a significant pressure drop causing NVH. In addition, where an air stream changes direction there can be significant turbulence in the flow also contributing to the overall NVH. 
         [0005]    In view of the above, it is apparent that there exists a need for an improved HVAC system having an improved duct capable of reducing NVH. 
       SUMMARY 
       [0006]    In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, the present invention provides a case and duct assembly for an HVAC system having reduced NVH characteristics. The duct assembly includes an outer wall defining a interior volume and including at least one ventilation port. Interior walls define at least two air passages. The first air passage has an input portion extending to the ventilation port such that a first air stream may flow from the input portion through the ventilation port. The second air passage has an input section extending to an output aperture intersecting the first air passage such that a second air stream may flow from the input section into the first air passage. A mixing zone is formed in the first air passage adjacent the output aperture where the first air stream mixes with the second air stream. Arranged across the output aperture is a slotted wall. 
         [0007]    In some embodiments, the first air passage includes a pivotable first air blend door upstream of the mixing zone. The first air blend door may pivot to any position between a fully open and a fully closed position to regulate airflow from the first air input portion into the mixing zone, thereby controlling a final temperature of the mixed air. Other embodiments may substitute or add an additional pivotable second air blend door upstream of the output aperture. The second air blend door may pivot to any position between a fully open and a fully closed position to regulate airflow from the second air input section into the mixing zone to provide an alternate means of controlling the final temperature of the mixed air. 
         [0008]    According to another aspect of the present invention, the duct assembly includes at least one additional passage, wherein an upstream segment of the additional passage intersects the first air passage between the ventilation port and the mixing zone. In one example, an optional mixed air blend door is disposed between the ventilation port and the mixing zone. The mixed air blend door may pivot between two orientations where one prevents airflow from entering the additional passage and the other prevents airflow from exiting through the ventilation port and directs the airflow entirely into the additional passage. Additionally, the mixed air blend door may pivot to any position between these orientations to control the amount of airflow directed through the ventilation port and into the additional passage. 
         [0009]    In yet another embodiment, the slots in the slotted wall are narrow slots having a length substantially greater than their width. In other examples, the narrow slots may have any appropriate orientation including, for example, substantially parallel, perpendicular or at an acute angle to a direction of the first air stream. 
         [0010]    Another aspect of the present invention includes an HVAC system having passive noise reduction for use in a motor vehicle. The system includes any of the duct assemblies described above wherein the ventilation port is arranged to ultimately open into a passenger compartment of the motor vehicle. This embodiment also includes at least one blower fluidly coupled to the duct assembly and providing airflow therein. The airflow is divided into the first air stream and the second air stream. An evaporator is disposed in the first air stream thereby cooling the first air stream and a heater core is disposed in the second air stream thereby heating the second air stream such that the resulting mixed air has a mixed or blended air temperature. 
         [0011]    Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a sectional view of a portion of a duct assembly including a slotted wall according to the present invention; 
           [0013]      FIG. 2A  is a sectional view of the duct assembly, generally taken along line  2 - 2  in  FIG. 1 , showing a first embodiment of the slotted wall; 
           [0014]      FIG. 2B  is a second embodiment of the slotted wall; 
           [0015]      FIG. 2C  is a third embodiment of the slotted wall; 
           [0016]      FIG. 2D  is a fourth embodiment of the slotted wall; and 
           [0017]      FIG. 3  is a sectional view of a heating, ventilation, and air conditioning system including the duct assembly of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring now to the drawings, a case and duct assembly embodying the principles of the present invention is illustrated therein and designated at  10 . As its primary components, the duct assembly  10  includes an outer wall  12  defining an interior volume, at least one ventilation port  14  and a plurality of interior walls  16  defining at least a first air passage  18  and a second air passage  22 . The ventilation port  14  may, for example, open into a passenger compartment of a motor vehicle (see  FIG. 3 ). The first air passage  18  extends from an input portion  20  to the ventilation port  14 . The second air passage  22  extends from an input section  24  to an output aperture  26  intersecting the first air passage  18 . Arranged across the output aperture  26  is a slotted wall  28 . 
         [0019]    In the embodiment shown, flowing air is provided and divided into at least a first air stream (indicated by the arrow  30 ) and a second air stream (indicated by the arrow  32 ). The first air stream  30  flows within the first air passage  18  from the input portion  20  downstream to the ventilation port  14 . The second air stream  32  flows within the second air passage  22  from the input section  24  downstream to the output aperture  26 . 
         [0020]    As indicated above, the second air passage  22  intersects and merges with the first air passage  18  upstream of the ventilation port  14 . This merging with the first air stream  30  occurs in a mixing zone  34  of the first air passage  18 , adjacent the output aperture  26  after the second air stream  32  flows through the slotted wall  28 . This forms a mixed airflow (indicated by the arrow  36 ). 
         [0021]    The merging of the two air streams  30  and  32  in the mixing zone  34  results in significant NVH being generated within the duct assembly  10 . One reason for the generation of NVH is the resulting pressure drop between the higher pressure second air stream  32  of the output aperture  26  and the lower pressure first air stream  30  of the mixing zone  34 . A second reason for the generation of NVH is turbulent air flow within the duct assembly  10 . Turbulent air flow can be particularly evident in, for example, the mixing zone  34  where the walls directing the air streams  30  and  32  impart disturbances into the flows. These disturbances can be amplified by the merging of the two already turbulent air streams  30  and  32 , resulting in significant turbulence in the mixing zone  34 , causing additional NVH. 
         [0022]    Also shown in the embodiment of  FIG. 1  are a plurality of optional blend doors. Depending on the specific application, one or more of these blend doors may be necessary to control the air flow and air temperature within and exiting the duct assembly  10 . More specifically, the first air passage  18  may include a first air blend door  37  located upstream of the mixing zone  34 . In the example shown, the first blend door  37  is pivotable about a first axis  38  between a fully open position, shown by the solid lines  40 , and a fully closed position, shown by the phantom lines  42 . Thus, this door  37  regulates the flow of first air stream  30  into the mixing zone  34 . Depending on the position of the first blend door  37 , the amount of flow of the first air stream  30  entering the mixing zone  34  can be varied to control, for example, a temperature of the mixed airflow  36 . It should be understood that the pivotable blend door  37  is but one embodiment of the optional blend doors. Any other appropriate door or orifice capable of controlling airflow may be used including for example, a butterfly door or a door that translates linearly rather than pivots about an axis. 
         [0023]    Other embodiments of the case and duct assembly  10  may include a second air blend door  44  and/or a mixed air blend door  52 . In the example shown, the second blend door  44  is disposed upstream of the output aperture  26 . The second blend door  44  is pivotable about a second axis  46  between a fully open position, shown by the solid lines  48 , and a fully closed position, shown by the phantom lines  50 , to regulate the flow of the second air stream  32  into the mixing zone  34 . The mixed blend door  52  is pivotable about a third axis  54  between a first orientation, shown by the solid lines  56 , an intermediate orientation, shown by the phantom lines  58 , and a third orientation, shown by the phantom lines  60 , to regulate the flow of the mixed airflow  36  between the ventilation port  14  and at least one additional passage  62 . 
         [0024]    The additional passage  62  intersects the first air passage  18  between the ventilation port  14  and the mixing zone  34 . When the mixed blend door  52  is in the first orientation  56 , none or negligible amounts of the mixed airflow  36  is permitted to enter the additional passage  62 . Conversely, when the mixed blend door  52  is in the third orientation  60  substantially all of the mixed airflow  36  enters the additional passage  62  as indicated by the arrow  64 . In the intermediate position  56 , a relative amount of the mixed airflow  36  enters both the additional passage  62  and the ventilation port  14 . Consequently, the amount of air passing through the ventilation port  14  is regulated (i.e. increasing the amount of air entering the additional passage  62  decreases the amount of air flowing through the ventilation port  14 ). In some examples, the additional passage  62  may direct at least part of the mixed airflow  36  so as to defrost a windshield of the motor vehicle (see  FIG. 3 ). In other examples (not shown), the additional passage  62  may direct the mixed airflow  36  to a floor of the motor vehicle. 
         [0025]      FIGS. 2A-2D  are taken along line  2 - 2  of  FIG. 1  and show various embodiments of the slotted wall  28 . In one example, the slotted wall  28  may be formed from a flat or arcuate section of the interior walls  16 . In another example, the slotted wall  28  may be formed from a flat plate across the output aperture  26 . 
         [0026]    Turning to  FIG. 2A , a first embodiment of the slotted wall  28  includes a plurality of slots  66  having a length  68  and a width  70  with the length  68  being substantially greater than the width  70 . In the example shown, the length  68  is approximately 7-8 times greater than the width and the slots  66  are oriented substantially parallel to the first air stream  30 . This arrangement reduces the pressure drop between the output aperture  26  and the mixing zone  34  and reduces turbulence in the mixing zone  34 , resulting in decreased NVH. 
         [0027]    It should be understood that the above relative dimensions and orientation are but examples of a single embodiment. Different proportions are possible depending on the exact geometry, materials and other needs of a particular application. 
         [0028]    A second embodiment shown in  FIG. 2B  illustrates multiple rows of slots  72  provided across the output aperture  26 . A third embodiment shown in  FIG. 2C  provides angled slots  74 . The angled slots  74  may be oriented at an acute angle  75  to the first air stream  30 . This embodiment also illustrates that a length  76  of one slot  74  may be different from the length  78  of another slot  74 . Finally, as best shown in  FIG. 2D , it is also possible for slots  80  to be oriented substantially perpendicular to the first air stream  30 . 
         [0029]    Turning now to  FIG. 3 , an HVAC system  90  for use in a motor vehicle  92  is shown. In this embodiment, features having the same function as described above have the same number as used in the embodiment of  FIG. 1 , only indexed by  100 . The HVAC system  90  includes a duct assembly  110  having an outer wall defining an interior volume and a plurality of interior walls defining at least a first air passage  118 , at least a second air passage  122 , and at least one additional passage  162 . 
         [0030]    The first air passage  118  extends from an input portion  120  to the ventilation port  114  that may, for example, open into a passenger compartment  94  of the motor vehicle  92 . This permits a first air stream  130  to flow from the input portion  120  out through the ventilation port  114  and into the passenger compartment  94 . The second air passage  122  extends from an input section  124  to an output aperture  126  that intersects the first air passage  118 , generally upstream of the ventilation port  114 . This permits a second air stream  132  to merge with the first air stream  130  at a mixing area  134 . A slotted wall  128  is arranged across the output aperture  126 . This slotted wall  128  may have any of the configurations described above and illustrated in  FIGS. 2A-2D . 
         [0031]    Additionally, the HVAC system  90  includes at least one blower  96  fluidly coupled to the duct assembly  110  and providing airflow within the duct assembly  110 . The airflow is divided within the duct assembly by any appropriate means into the first air stream  130  and the second air stream  132 . The HVAC system  90  further includes a cooling unit  98  and a heating unit  100 , respectively disposed within the input portions  120  and  124  of the first and second air passages  118  and  122 . 
         [0032]    The cooling unit  98  may be any conventional unit configured to cool the first air stream  130 . The cooling unit  98  may include, for example, an evaporator fluidly coupled to other components of an air conditioning system (not shown) of the motor vehicle  92 , or thermoelectric devices powered by an electrical system (not shown) of the motor vehicle  92 . Likewise, the heating unit  100  may be any conventional unit configured to heat the first air stream  132 . The heating unit  100  may include, for example, a heater core fluidly coupled to other components of an engine cooling system (not shown) of the motor vehicle  92 , or electric heaters powered the electrical system. Obviously, the units  98  and  100  could be reversed in their locations. 
         [0033]    Consequently, a cooled first air stream  130  and a heated second air stream  132  are mixed within the mixing zone  134  in the first air passage  118 , forming a mixed air flow  136 . The mixed air flow  136  may have any appropriate temperature and flow distribution necessary for a particular set of conditions. The necessary temperature and flow distribution may be provided by adjusting one or more blend air doors  137 ,  144 , and  152 , as analogously described above. 
         [0034]    As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.