Abstract:
An air filter assembly for a motor vehicle has a filter housing and an air filter disposed in the housing. The housing has a liquid outlet downstream of the filter and a filter bypass passageway is provided for enabling liquid entering at an air inlet to flow past the filter and exit through the outlet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to air filter for a vehicle ventilating or air conditioning unit. 
     2. Description of the Related Art 
     It is now common to provide passenger vehicles such as cars with air conditioning units. Such units typically comprise a housing having a first inlet in use disposed in communication with the interior of the vehicle passenger compartment and a second air inlet for inducing ambient air. The housing contains an evaporator whose function is to cool the air which enters via one or other of the inlets, and the housing has an air outlet for cooled air. As is known to those skilled in the art, the cooled air is usually passed to a heating and distribution unit for supply to different openings within the passenger compartment. 
     When air of high humidity is passed through the cooling evaporator, the moisture in the air condenses out and it is therefore necessary to provide a liquid outlet downstream of the evaporator, and normally near to or in the bottom wall of the housing so that the condensate can be suitably disposed of. 
     Air conditioning units are of particular utility in high temperature high humidity parts of the world, for example tropical parts of the world. A difficulty may arise when high rainfall leads to water being induced through the external air inlet. Unless a technique is devised for guiding water induced in this way out of the air conditioning unit, the water will collect in the housing and stagnate thereby giving rise to smells, will prevent the filter member from working properly or may eventually leak into the passenger compartment. 
     It is accordingly an object of the present invention to provide an air conditioning unit which is capable of coping with incoming rain. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided an air filter assembly for a motor vehicle comprising filter housing and an air filter, the filter housing having an air inlet and an air outlet, the air filter being disposed in said filter housing, and the housing having at least one liquid outlet downstream of the filter wherein the assembly has a filter bypass passageway for enabling liquid entering at said air inlet to flow past said filter to said liquid outlet. 
     Preferably, the filter housing further comprises an evaporator disposed downstream of the filter. 
     Preferably the housing has a lower wall and the air filter has a lower portion spaced from the lower wall to define said passageway therebetween. 
     Advantageously the air filter has a total area more than 10 times the area of said passage. 
     Conveniently the filter assembly has an upper wall, opposing sidewalls and a lower wall, said lower wall defining an opening therein, a filter module having a portion extending through said opening, the filter module further having a face plate sealingly abutting an outer face of said lower wall, said filter module comprising a frame having an outer perimeter portion engaging the sidewalls and said upper wall, said frame supporting a filter member spaced from said lower wall to define said passage. 
     Advantageously said frame comprises a transverse web spaced from the face plate and defining therebetween a through hole. 
     Conveniently the air conditioning unit further comprises plural supporting web portions disposed between the face plate and said transverse web. 
     Preferably the filter member has a total area more than 30 times the area of said passage. 
     Preferably the outer perimeter portion has an outwardly-directed flange portion and the housing has a counterpart slot. Preferably the lower wall has a depressed region forming a trough. 
     Conveniently said trough is substantially filled with a closed foam material. 
     Advantageously said closed foam material comprises liquid guide passageways for directing the liquid to said liquid outlet. 
     An embodiment of the invention will now be described by way of example only, with respect to the accompanying drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a sectional view through a first embodiment of an air filter assembly in accordance with the invention; 
     FIG. 2 shows a cross-sectional view through a second embodiment of an air filter assembly in accordance with the invention; 
     FIG. 3 shows a perspective view of a first filter module for use with the embodiment of FIG. 2 and; 
     FIG. 4 shows a perspective view of a second embodiment of a filter module for use with the embodiment of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the various figures like reference numerals refer to like parts. 
     Referring first to FIG. 1, the first embodiment  100  of an air filter assembly consists of a casing  101  hereinafter referred to as “a filter housing” and an evaporator  102  disposed to engage upper  120  and lower  121  walls of the evaporator housing  101 . It will be understood that the evaporator  102  also extends laterally to engage sidewalls (not shown) of the filter housing  101 . Thus the filter assembly here is part of an air conditioning unit. 
     The filter housing  101  also defines first and second air inlets  103 ,  104  and an air outlet  109 . In use, the first air inlet  103  which is generally upwardly open receives air from outside a vehicle in which the air conditioning unit is mounted and the second air inlet  104  connects to the interior of the passenger compartment of the vehicle. To select the mode of operation of the air conditioning unit, namely whether air is to be induced from outside or to be re-circulated from within the passenger compartment there is provided a mode door  105  pivoted on one side and capable of moving between the first position shown in FIG. 1 where it sealingly closes the second air inlet  104  and a second position shown in dotted lines as  106  where it sealingly closes the first air inlet  103 . 
     The air outlet  109 , as known to those skilled in the art, is connected to a fan incorporated within a heater and distribution unit, not shown. 
     On the upstream side of the evaporator  102  there is disposed an air filter  107  which removes particulate matter from air entering the air conditioning unit. Downstream of the evaporator  102  the lower wall  121  of the evaporator housing  101  is depressed downwardly to form a trough portion  110  having a fluid outlet  108 . 
     In normal use, the above discussed fan is operated to cause air to enter via a selected one of the two air inlets  103 ,  104  and the air passes through the filter  107  and then through the evaporator  102 . A refrigerant is supplied to evaporator  102  to cause the air passing through it to be cooled and, as known to those skilled in the art the cooling results in moisture in the air condensing out. The condensate is collected in the trough  110  and passes out of the air conditioning unit through the liquid outlet  108 . The cooled air passes out of the outlet  109  for distribution to the passenger compartment of the vehicle. 
     A problem may arise in conditions of high rainfall or where the vehicle of concern passes through water. In this case, unless special measures are taken to prevent water ingress to the first air inlet  103 , such water may enter through the first air inlet  103 . Further reference to FIG. 1 shows that the filter  107  does not extend across the full height of the evaporator housing  101  but instead has a lower wall  111  which is spaced from the lower wall  121  of evaporator housing  101  so as to provide a passageway allowing any liquid to pass beneath the air filter. Such water can pass through the evaporator into the trough  110  and out through the liquid outlet  108 . To provide adequate drainage the outlet in the embodiment allows around 8 L/minute to pass through at 
     Failure to provide such a passage can result in the water level upstream of the filter rising sufficiently to flow out through the second air inlet  104  when the mode door  105  is switched over. Alternatively the water may stagnate causing smells in the system. 
     It will be seen from FIG. 1 that the filter  107  is suspended from the top wall  120  of the evaporator housing  101 . 
     Referring now to FIG. 2, a second embodiment  200  is shown. This second embodiment has a filter module  210  which is inserted through an opening in the lower wall  121 . The filter module is more clearly seen in FIG.  3 . 
     Referring now to FIG. 3, filter module  210  consists of a frame having an outer perimeter portion  220  which extends from a face plate portion  221  to define a first generally rectangular opening  222  which supports a filter member  223 . The filter member in this embodiment is netted polypropylene. The frame together with the face plate further comprises a transverse web portion  224  generally parallel to the face plate and spaced from it to define a passageway  230  between the face plate  221  and the web portion  224 . Further reference to FIG. 3 shows that three supporting web portions  231  extend from the face plate  221  to the web portion  224  to provide four through holes following the passage  230 . 
     On one side of the perimeter portion  220  there is a lipped flange portion  226  which engages with a corresponding slot in the evaporator housing  200 . The slot runs along the sidewalls of the housing  200  and also along the top wall  120 . Clips are used to secure the filter module  210  in sealing engagement with the lower wall  121  of the evaporator housing  201 . Alternatively, screws or any other suitable fixing could be used. 
     It will be appreciated by those skilled in the art that the relative dimension of the passage  230  to the area of the filter part is important. In exactly the same way, the dimension of the spacing between the lower wall  111  to the lower wall  121  in relation to the size of the filter in the embodiment of FIG. 1 is important. If the area of the passageway is too great then air will be drawn through the passageway rather than passing through the filter. It is clearly desirable that air is predominantly drawn through the filter. To achieve this it has been found that a ratio of 1:32 is desirable. 
     It will understood by those skilled in the art that the trough portion  110  of the air conditioning unit represents an increased surface area which by virtue of being cold may allow condensation to form on the outside especially under humid conditions eg tropical conditions. To avoid this, the trough may be filled with an insulating material, preferably a closed cell foam which will not itself absorb liquid. Materials that absorb liquid may themselves give rise to smells in the system. 
     A second embodiment  310  of the air filter module will now be described with reference to FIG.  4 . 
     A comparison between FIG.  4  and FIG. 3 shows that the second air filter module  310  is similar to the first module  210  with the exception of the opposing sidewalls of the outer perimeter portion of the frame. In the second filter module the sidewalls are formed to generally follow the zig-zag contours of the filter member  223  so that the sidewall consists of a series of V-shaped lands  311  with intercalated V-shaped cut-out portions  312 . 
     The effect of the cut-out portions is to provide flexibility to the filter member whilst still providing structural integrity. Thus, a force applied to the face plate  221  either to insert or retract the filter module will be transferred to the whole filter module. 
     The perimeter portions of the frame are made from a plastics material, typically polypropylene, and the cut out portions  312  allow the filter module to be more easily inserted in a restricted access situation. Specifically, the face plate may be rotated about a transverse axis so that the filter module during insertion or extraction assumes a generally L shape. 
     The supporting web portions  231  extending from the sidewalls of the outer perimeter portion of the frame and the transverse web portion  224  create a stiff extension of the filter member. When removing a filter from its housing, the maximum constraints are faced during the initial part of the extraction. This is due to maximum lateral friction constraints and means that the highest effort is needed at this time. As is clear to those skilled in the art, after the range which requires the maximum effort, the frictional values drop rapidly and extraction movement speeds up. If the filter member is directly secured to the face plate, the movement of extracting the filter from the housing and at the same time rotating it causes a serious risk of damage. By provision of the supporting web portions  231  which creates a stiff extension the first part of extraction must be performed in line with the support slots in the housing and this prevents filter damage.