FIELD OF THE INVENTION The invention relates generally to filtration systems, and particularly to a method and apparatus for air filtration in a vehicle cabin.

BACKGROUND OF THE INVENTION A recent development in the automotive industry is air filtration systems in the vehicle. Due to increasing levels of pollution in the environment generally, and particularly in high vehicular traffic areas, such systems are desirable. These filtration systems may include individual filters associated with the HVAC vents located throughout the vehicle. Alternatively, intake filterε could be employed in the area of the vehicle where outside air is drawn in. In either case, the filters are designed to filter out undesirable particulate matter and other pollutants while not significantly affecting the air flow into the vehicle which is used for environmental and comfort purposes (e.g. defrosting, heating, air-conditioning, etc.) . Thus, it is desirable to provide filtered air to the vehicle cabin but not at the expense of losing the air flow and its attendant benefits.

As the filters presently in use in these systems begin to accumulate dirt and debris from filtering the air flowing through them, they will begin to become clogged. Of course, the air flow through a clogged filter may be significantly lower then the air flow through an unclogged filter. Moreover, other environmental conditions may lead to decreased air flow through the filter. For filters located downstream of blower units in the cabin, with the air conditioning activated, super cool air is delivered through the filter to the cabin. Any condensation of moisture in the air on the filter may subsequently be frozen by the cool air flowing through it. Of course, the presence of such

frozen condensation would tend to impede air flow through the filter. For intake filters located external to the cabin, ambient environmental conditions may cause accumulation or freezing of moisture in the filter. Thus, while these filters perform the desirable function of filtering the air, the air flow through them may be impeded in certain situations.

SUMMARY OF THE INVENTION Accordingly, it is the aim of the invention to provide an air filtration system for a vehicle cabin that can also maintain a desired air flow into the cabin for all conditions.

In keeping with that aim, it is a primary object of the invention to provide a filtration system including means for bypassing the filtration system when the status of the filtration system would otherwise impede airflow.

It is a related object of the invention to provide a mechanism wherein air may be diverted around the filter when it becomes clogged or otherwise begins to impede air flow.

In accordance with these and other objects, there is provided an apparatus and method for filtering air to a vehicle cabin while always maintaining a sufficient air flow to the cabin. Toward that end, a filter assembly is disposed in a flow of forced air which passes through the assembly, and eventually exits through a vent into the vehicle cabin. The filter assembly may either be an intake filter assembly disposed outside the cabin, or be an outlet filter assembly associated with individual vents in the cabin. The filter assembly includes a filtration media having a microporous structure for filtering airborne impurities from the air flow. The flow of forced air through the filtration media defines a first flow path. A diverting opening is provided that is disposed adjacent to the filtration media. Flow of the forced air through the diverting opening defines a second flow path. The filter assembly also includes a closure

for the diverting opening. This closure is movable between a closed position, wherein flow through the diverting opening is prevented, and an open position wherein flow through the diverting opening is allowed. The closure moves from the closed position to the open position in response to a predetermined decrease in the flow rate in the first flow path caused by clogging or other obstructions in the filtration media. In this way, filtered air is provided to the vehicle cabin until the air flow through the filtration media falls below a predetermined value. At that point, the air flow is diverted around the filter and unfiltered air is delivered to the cabin at an acceptable flow rate.

The method according to the invention comprises generating an air flow from outside a vehicle into the cabin, and filtering that air by providing a filtration media between the exterior source of the air flow and the cabin. The rate of air flow through the filtration media is sensed to determine when the flow rate falls below a given value. In response to that event, the air flow is diverted to bypass the filtration media thereby providing unfiltered air to the cabin at an acceptable rate of flow.

According to a preferred embodiment of the apparatus of the invention, the closure is pressure sensitive, and is thus responsive to either an increase in localized pressure or a localized negative pressure caused by the reduced flow through the filtration media. An increased localized pressure on the closure will result from clogging of the filtration media if the closure is located downstream of the blower supplying forced air to the cabin. A negative localized pressure will result if the closure is located upstream of the blower, since reduced flow through the filtration media would result in an increased draw on the closure. The closure device may be a rotating flap to which a torsion spring is coupled for exerting a biasing force tending to move the closure toward the closed position. The increased localized

pressure or localized negative pressure (again depending on the location of the closure relative to the blower) exerts force on the flap which is sufficient to overcome this biasing force allowing the closure to move to the open position. Other structures for biasing the closure to the closed position are disclosed.

The apparatus and method according to the invention advantageously provide filtered air to the cabin under most circumstances. However, when clogging or other obstructions in the filtration media causes the flow rate of air to fall below a predetermined value, the method and apparatus provide for diversion of the air flow around the filtration media. The air is then delivered to the cabin at an acceptable flow rate, but is not filtered. An acceptable rate of air flow is thus always delivered to the cabin, and is also advantageously filtered under normal operating conditions. These and other advantages of the invention will be discussed in greater detail in the specification which follows.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in reference to certain preferred embodiments, as shown in the attached drawings, wherein: Fig. 1 is an elevational view of a vehicle, including a forced air delivery system incorporating a filter assembly according to one embodiment of the invention; .

Fig. 2 is a top view of the vehicle and filtering system shown in Fig. 1;

Fig. 3 is an exploded view of a vent assembly including a filter assembly according to one embodiment of the invention;

Fig. 4 is a section view of the vent assembly of Fig. 3 in combination with a filter assembly according to an embodiment of the invention;

Fig. 5 is a similar view of Fig. 4, but showing diversion of air through a diverting opening according to

a feature of the invention.

Fig. 6 is an exploded view of a vent housing and filter assembly according to an alternative embodiment of the invention; Fig. 7 is a section view of the vent housing showing in Fig. 6, in combination with the filter assembly according to the invention;

Fig. 8 is a section view like that shown in Fig. 7, but showing diversion of the air flow according to feature of the invention;

Fig. 9 shows a magnetic latch for the closure according to an alternative embodiment of the invention;

Fig. 10 is a perspective view of a vehicle showing an illustrative location for cabin air intake ports; Fig. 11 is an elevational view of a series of cabin air intake ports;

Fig. 12 is a section view of one of the cabin air intake ports and an associated filter;

Fig. 13 is a section view of a diverting opening and associated closure according to an embodiment of the invention;

Fig. 14 is an exploded view of a preferred embodiment of the diverting opening and associated closure; and Fig. 15 is a section view of a diverting opening and closure similar to that of Fig. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention will be described with reference to the preferred embodiments, it will be obvious to those of ordinary skill in the art that variations of these preferred embodiments may be used and it is intended that the invention may be practiced otherwise than as specifically described herein. Accordingly this invention includes all modifications and equivalents encompassed within the spirit and scope of the invention as defined by the appended claims.

Filtration systems typically now being used in

vehicles may include filters located immediately adjacent to the vent in the vehicle cabin, thus filtering air that has already passed through a blower for providing forced air to the cabin. Such filters will be generally referred to herein as outlet filters. As an alternative to filtering the air at each outlet, the air may also be filtered at an inlet. Since vehicles typically include a series of closely-spaced common inlets to provide air to the blower, this allows use of a single filter assembly for the entire vehicle. Such intake filter systems also fall within the scope of this invention, and are described herein.

Fig. 1 shows a plan view of an air delivery system for vehicle 10 which includes outlet filters. Vehicle 10 illustratively includes a front blower 11 and a rear blower 12 connected via conduits 15 to a plurality of vents disposed throughout the vehicle. Different vents may have different structures depending on their location and function within the vehicle. For example, vehicle 10 shown in Figs. 1 and 2 has defrost vents 20, horizontal vents 25 for blowing air horizontally, and vertical vents 30 for blowing air vertically. Of course, one skilled in the art will appreciate that a wide variety of duct work and vents may be used for the purpose for providing forced air to a vehicle cabin.

The air provided by the blowers to the cabin through these vents is filtered by providing a filter assembly, according to one embodiment of the invention, which is associated with each of the vents. Fig. 3 shows an illustrative example of a filter assembly according to one embodiment of the invention. A vent housing 40, including a connector 41 for connection to a forced air conduit 15 receives the filter assembly 50. A vent grill 42 may be disposed in the vent housing 40 over the filter assembly 50. The vent 40 shown in Fig. 3 is a vertical vent like the vents 30 shown in Figs 1 and 2.

In the present embodiment, filter assembly 50 includes a filtration media in the form of a membrane 55.

Referring to Fig. 4, it can be seen that with the filter assembly disposed within the vent houεing 40, forced air from the blower passes through the filtration membrane 55 and out the vent cover 42. In this way, air provided from the blowers is filtered before it enters the vehicle cabin. A variety of filtration media may be used to provide the desired filtration, including high efficiency wet laid media or high efficiency electret media. A presently preferred filtration membrane is a media manufactured by the Westec division of Lydall and identified as TR 1745-C Polyester Thermal Bonded. Other polyester or glass media could be used. This filtration media is capable of removing 80% of 3 micron and larger particles from the air passing through it while still providing an acceptable air flow to the cabin. Additions to the media, such aε carbon, may also be included to enhance filtration. Further, as an additional feature of the invention, the media may include an anti-microbial coating. A variety of coating could be used. Any coating, however, should be EPA registered as an air filtration product. Further, it should not exhibit any off-gassing from the media, or otherwise separate from the media. We envision an anti-microbial coating being applied which would exhibit less than 40% growth on either side of the media, as tested in an environmental chamber test.

As the filter membrane 55 filters particles and other undesired pollution from the air entering the cabin, the membrane will eventually begin to become clogged. This clogging will result in reduced air flow through the membrane. Further, certain environmental conditions in the vehicle may also cause a reduction in flow through the membrane. For example, the passage of chilled air-conditioned air through membrane could cause frozen water particles to form within the membrane, thus inhibiting flow through it. Continued clogging or other obstructions in the membrane will eventually reach the point where the air flow through it is unacceptable.

That is, the air flow through the filter is used for a variety of purposes within the vehicle, such as climate control and for safety purposes, such as preventing fog build up the windshield. The uses of the air flow all require some minimum required flow rate, which is designed by most vehicle cabin manufacturers to be between 10% and 20% loss. Most car cabin systems run at maximum volume of 300-350 SCFM (standard cubic feet per minute) . To prevent clogging or other obstructions in the filtration media from allowing the flow rate to fall beneath the desired minimum value, the filter assembly according to the invention is provided with a diverting opening, designated by reference numeral 60 in Fig. 5. Coupled to this diverting opening is a closure 70. According to the invention, the closure is movable between a closed position such as that shown in Fig. 4, wherein flow through the diverting opening is prevented, and an open position such as that shown in Fig. 5 wherein flow through the diverting opening is allowed. According to a significant aspect of the invention, the closure 70 is designed to open only when the flow through the filtration membrane 55 falls below the minimum required flow rate for the vehicle cabin. Thus, when the filtration membrane 55 is not clogged or otherwise obstructed, as in Fig. 4, air from the blower follows a first flow path through the membrane 55. However, upon clogging of the membrane 55 as in Fig. 5, the forced air follows a second flow path through the opened diverting opening 60 and out the vents 42. In that way, filtered air is typically delivered to the cabin at a flow rate above the minimum required flow rate. However, when the flow rate of the filtered air falls below the minimum required flow rate, the closure 70 opens diverting opening 60 and allows unfiltered air, above the required minimum flow rate, to flow into the cabin through the vent cover 42.

Closure 70 is designed to only open when flow

through the filtration membrane 55 falls below the minimum required value. Toward that end, and according to the present embodiment, the closure 70 is in the form of a flap covering the diverting opening 60, as is most clearly in Fig. 3. Closure 70 is normally held in the closed position by means of a resilient member illustratively in the form of a torsion spring or springs 75. In the present embodiment, the torsion springs 75 are coupled both to an interior wall of the opening 60 and the inside surface of the closure 70, as seen most clearly in Fig. 5. The torsion spring 75 exerts a biasing force on the closure 70 which tends to rotate it to the closed position of Fig. 4. This force is overcome, however, by increased presεure working on the inner face 71 (Fig. 4) of the closure 70. This increased pressure results from clogging or other obstructions in filtration membrane 55 preventing adequate flow through the membrane. The resulting localized increased pressure on the face of 71 results in a force sufficient to overcome the resilient force of the spring 75 which biases the closure 70 toward the closed position. Thus, by properly εelecting the dimension of the closure 70, and the stiffness of the torsion spring 75, the necessary presεure for opening of the closure 70 can be selected. Of course, this pressure can be related back to the minimum required flow rate necessary for forced air being delivered to the cabin. Accordingly, when obstructionε in the membrane 55 cauεe the flow rate to fall below this minimum required value, closure 70 will open and provide unfiltered air to the cabin above the minimum required flow rate.

While a torεion εpring has been shown coupled to the closure 70 for the purpose of biasing it toward the closed position, other such mechanisms could be used. An example of an alternative mechanism is a magnetic latch like that shown in Fig. 9. Fig. 9 shows a diverting opening 60 that is normally closed by a closure 70 as in the previous embodiment. Fig. 9 shows an air flow

direction that is reversed from that shown in Figs. 4 and 5. That is, the mechanism shown in Fig 9. would be used in a vertical vent intended for blowing air upwards in a vehicle cabin. To normally maintain the closure 70 in the closed position, the magnetic latch comprised of metal strip 80 and magnet 85 is provided. Of course, the location of these two members could be reversed. With the closure 70 in the closed position, strip 80 and magnet 85 are in engagement, and the magnet 85 exerts a magnetic force on the cloεure tending to maintain it in the closed position. Reduced air flow through the filtration membrane 55 will cause increased presεure againεt the cloεure member 70. This increaεed preεεure will eventually tranεlate into a force sufficient to overcome the magnetic force between magnet 85 and the metallic strip 80 thus allowing closure 70 to open. In the embodiment shown in Fig. 9 subsequent closing of the closure 70 occurs by virtue of gravity when the condition causing reduced air flow through the filtration membrane 55 is alleviated thus allowing the minimum required air flow through the membrane, and eliminating the need for the closure 70 to be open. In a further alternative embodiment, the magnetic latch could be eliminated all together, and the closure 70 could be designed to act only by gravity. That is, gravity would hold latch member 70 closed in Fig. 9, and a force greater than that gravitational force could cause closure 70 to open according to the invention. Weights could be added to the closure 70, as desired, to increase the force necesεary to open the closure. Further, the closure 70 could be disposed in a vertical position and comprise a flap of material hanging down over the diverting opening; either with or without weightε at the free end. It will alεo be apparent to those skilled in the art that the apparatuε according to the invention iε readily adaptable to a variety of εpecific vent structures besides that shown in Figs. 4 and 5. For example, an

embodiment of the invention for use in a horizontal vent is shown in Fig. 6-8. In this embodiment, the filter aεεembly 100 is designed to fit within a vent housing 110, behind a vent grill 120. Referring to Fig. 7, filter assembly 100 includes a housing 130, which receives the filtration member 155 which, according to the present embodiment, is unitary as opposed to being in two portions as in the previous embodiment. Located upstream of the filtration membrane 155 is the diverting opening 160 which, according to the present embodiment, is dispoεed in the housing 130. As in the prior embodiment, a closure 170 normally closes diverting opening 160 to define a firεt flow path for the forced air through the filtration membrane 155. The cloεure 170 is responsive to a decrease in the flow rate through the membrane 155 below the minimum required flow rate into the cabin to move from the closed poεition of Fig. 7 to the open poεition of Fig. 8. Aε before, a torεion εpring 175 iε coupled to the closure member 170 to normally bias it toward the closed position of Fig. 7. With the closure of 170 open, the air flow follows a second flow path through diverting opening 160 around the housing 130, and out through the vent grill 120.

An alternative embodiment of the filter asεembly according to the invention iε εhown in Figs. 10-13. The embodiment of these figures is an intake filtration εyεtem as opposed to an outlet filtration as previously described. Typically, vehicles include a series of closely-εpaced openings or inlet ports that serve as an inlet for air to be supplied to the cabin. External air thus flows through the inlet ports and through a blower into the vehicle cabin. Since the air drawn in through the inlet ports is brought through a blower and supplied to the cabin, it will be referred to herein aε a flow of "forced air" in regard to both inlet and outlet filtration systems. By this term it is simply meant that the air is positively drawn through the inlet ports by the blower. The closely spaced inlet ports are typically

disposed near the windshield of a vehicle beneath a grating which keeps out large objects. The grating G and general position of the inlet ports is shown in Fig. 10. Typically, the inlet ports are dispoεed on a vertical wall beneath the grating. Fig. 11 shows the inlet ports 200 through 205 in an elevational view. As can be seen from that figure, the 6 ports may illustratively be broken up into two mirror-imaged setε of three portε each. To provide for filtration of incoming air through theεe inlet ports, some or all of the inlet ports may have a filtration media illustratively in the form of a filtration membrane as previously described. According to this embodiment of the invention, the four center inlet ports (201-204) include εuch filtration membraneε. Ports 200 and 205, on the other hand, include diverting openings according to a further aspect of the invention.

The section view of Fig. 12 shows one of the filtration membranes in place within inlet port 201, along with the surrounding structure. The filtration membrane 208 is received within a housing 210 adapted to engage within the inlet port 201. The inlet port 201 is, in turn, formed within a vertical wall of the wet plenum 212 which iε disposed beneath the grates (G in Fig. 12) that were shown in Fig. 10. A dry plenum 214 is diεpoεed behind the wet plenum 212. The dry plenum encloses the filter or diverting opening asεemblies associated with each of the openingε 200-205 and leads from there to the blower. Accordingly, all six of the inlet openings 200- 205 are subject to the draw of the blower pulling air from the outside, through the dry plenum and into the blower. Since opening 201-204 include filtration membranes, forced air from the outεide iε filtered before approaching the blower, and being delivered to the vehicle cabin. The flow of forced air through theεe filtration membraneε defineε a first flow path.

As the filters become clogged due to use or environmental conditionε, however, diverting openings

diεpoεed within inlet ports 200 and 205 will open, thus defining a second flow path for the forced air. As mentioned above, the blower draws on all of the inlet of ports 200-205. When the filters asεociated with portε 201-204 are not clogged or otherwiεe obεtructed, air iε pulled by the blower through theεe filters. However, obstruction of these filters causeε reduced pull on portε 201-204, and an increased draw in the form of a negative presεure on ports 200, 205, with which the diverting openings are associated. Accordingly, the localized negative presεure that forces the diverting openings to their open position is provided for by the increased draw from the blower due to reduced flow through filtration membrane imports 201-204. The diverting opening asεociated with inlet port 200 is shown in side sectional view in Fig. 13. As in the diverting openings from the previous embodiments, the diverting opening in Fig. 13 includes a closure 240 which closeε the opening 230. A torεion εpring 245 may illuεtratively be coupled to closure 240 to bias it toward the closed position of Fig. 13. Reduced flow through the remaining filters in the plenum causeε a large enough negative pressure on closure 240 to overcome the cloεing force of the torεion spring, thus allowing closure 240 to open and allowing air to flow therethrough. As before, the strength of the torsion spring 245, and the exact dimenεions of the closure 240 may be modified as necesεary to change the force necessary to open the closure 240. Such programming of the opening force required on the closure may be important in the situation where the dry plenum is configured such that the draw on all six inlets ports 200-205 is not the same. For example, one type of dry plenum is configured such that the draw comes from a portion of the dry plenum adjacent one end of the line of closely spaced inlet portε 200-205. For example, the conduit to the blower which serves aε a εource of the draw on the portε 200-205 may be adjacent to port 205.

Port 201 will feel significantly lesε draw, particularly because filtration membraneε will be in place on each of the remaining ports 201-204. Accordingly, a significantly smaller opening force may be required for the diverting opening associated with port 200 then for port 205. Further, some openings may need to be provided in the filter housingε aεsociated with the remaining ports 201-204 to allow diverted air to flow through port 200 to the conduit forming the source of the draw in such a configuration. Other modificationε both to the plenum, and to the filter and diverting opening assemblieε juεt deεcribed, will be apparent to one εkilled in the art, yet εtill remain within the εcope of the preεent invention. A preεently preferred embodiment of the diverting opening and aεεociated cloεure is shown in exploded view of Fig 14. A sectional view of a similar port is shown in Fig. 15, the two figures differing only in the overall shape of the housing, but not differing in regard to the detail associated with the closure. The diverting opening 300 is disposed within a housing 305 illustratively received within the dry plenum associated with an inlet port such as 200 or 205 in Fig. 11. A hinged cloεure 310 normally cloεes the opening 300. As can be seen from Fig. 14, closure 310 includes two hinge collars 311 and 312. These hinge collars engageε hinge pinε 301 and 302 which are integrally formed with houεing 305. Associated with the hinge pins are recesses 303 and 304. The assembled arrangement of the hinge pins 301, 302 recesses 303, 304 and hinge collars 311 and 312 provides a rotating hinge with very cloεe tolerances to prevent leakage past the hinge when closure 310 is in the closed position over opening 300. The hinge pin 301, recess 303 and hinge collar 311 may be seen more clearly in the section view of Fig. 15. With the closure 310 in the closed position, the perimeter of the main body closure of 310 engages a flat peripheral land 307 extending around the perimeter of the opening 300.

As in previouε embodimentε, cloεure 310 iε biaεed towards the closed position by means of torsion springε, one of which is shown at 320 in Fig. 14 (2 torsion springs are preferably used) . To retain the two legε 321 and 322 of the torsion spring on the housing 305 and closure 310 respectively, spring receiving lands are provided. Spring receiving land 331 is provided on closure 310, and spring receiving land 332 iε provided on houεing 305, aε can alεo be εeen in Fig. 15. The lands comprise built up projections with central troughs (such as 333 on land 331) for receiving the respective legs of the torsion spring 320. The troughs in the spring receiving lands prevent any displacement of the legs of the torsion spring thus leading to greater positional stability of the torsion springs.

This stability is further enhanced by the presence of a spring stabilizer 340. According to the present embodiment, spring stabilizer 340 is in the form of a cylindrical post 341 with mounting projections 342 and 343. Stabilizer 340 also includes spring-receiving projections 345 and 346. Spring stabilizer 340 is mounted in housing 305 by means of the mounting projectionε 342 and 343 being received in mounting holeε 352 and 353 reεpectively. Mounting projection 342, as received in mounting hole 352, can also be seen in Fig.

15. As can be seen from Fig. 14, the mounting postε have central εlitε which provide a cantilever action to the two halveε of the projection on either εide of the εlits. Further, the heads of the mounting postε are tapered. Accordingly, aε the mounting poεts are inserted into the receiving holes in the housing 305 the tapered head forces the two halves of the projection together until the head completely pasεes through the mounting openings 352, 353. Once the head of a mounting projection passeε through the opening, the two halveε εnap apart locking the mounting poεt in place within the opening, thereby. As will be appreciated by one skilled in the art, the spring stabilizer 340 will need to be formed of a

material having εufficient resiliency to provide this function. According to the presently preferred embodiment, spring stabilizer 340, and indeed housing 305 and closure 310, are preferably formed of plastic material such as ABS or PVC. Rubber or a fiberglasε resin could also appropriately be used. The plastic parts are preferably formed by injection molding.

Spring-receiving projections 345 and 346 have a similar structure and function to mounting projections 342 and 343. That is, the expanded, tapered head of the spring-receiving projection is designed to compress as the central opening of the torsion spring is pasεed over the head. Once the torsion spring has completely paεεed the head, the two halveε εnap outwardly locking the torsion spring in place between the expanded head and the annular flat surface at the ends of the central cylindrical post 341. The receipt of the torsion springε on the spring-receiving projections of the spring stabilizer 340 prevents any unwanted displacement of the torsion springs as the cloεure 310 moveε between itε open and cloεed poεitionε with respect to the diverting opening 300. The enhanced stability of the torεion εprings in turn leads to more accurate programming of the opening force required to move closure 310 from the closed to open poεition.

The filter aεεemblies according to the various embodiments of the invention thus advantageously allow filtration of forced air to the cabin of a vehicle under most circumstanceε. However, aε clogging or other obεtructions in the filtration media reduces the air flow to the cabin below a required air flow, the apparatus provides a second flow path around the filtration media such that an unfiltered air flow at or above the minimum required rate can be maintained into the cabin. For this purpose, the filter asεembly according to the invention includes at least one diverting opening which is normally closed by a closure. However, the closure opens upon a reduction in a flow rate in the first flow path through

the media. Subεequent replacement of the media, or εome other clearing of the obεtruction in the media which allowε flow above the minimum required level back through the media, causes the closure to reclose thus reestablishing the first flow path as the flow path for the forced air.

The method according to the invention comprises first generating an air flow from outside the vehicle into the cabin. The air is then filtered by providing a filtration media between the outside source of air and the vehicle cabin. The rate of the air flow through the media is then εenεed to determine when the flow rate fallε below the minimum required flow rate for the cabin. When thiε occurε, the air flow iε automatically diverted to bypaεs the media and supply unfiltered air, at the deεired flow rate, to the cabin. The steps of senεing the flow rate through the filter media and diverting the air flow iε performed by moving a pressure sensitive closure from the closed position to an open position in responεe to either an increaεed localized pressure or a localized negative pressure (depending upon whether the closure is located downstream or upstream of the blower) caused by the reduced flow rate through the media. Further, the closure iε automatically closed when the localized presεure is again reduced or increased by the flow rate through the media surpasεing the minimum required flow rate.

The apparatus and method of the invention thus advantageously provide filtered air to a vehicle cabin, while always assuring a flow rate in excess of the minimum required flow rate. As will be appreciated by those skilled in the art, this invention may be practiced otherwise than as specifically disclosed herein. The invention is intended to cover all modifications and equivalents as fall within the scope of the appended claims.