Abstract:
Oil entrained in purge air from a vehicle air dryer is directed through a purge air cleaner to remove the oil before discharge of the purge air to the environment. An absorbent material, perferably hydrophobic, is enclosed in the purge air cleaner, which may be safely disposed. Alternatively, oil can be extracted from the absorbent media and thereby recycled. By providing a spin-on type canister, the absorbent media can be easily replaced and serviced.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an air dryer assembly for a compressed air system, such as a compressed air braking system for commercial vehicles, and more specifically to an air dryer with a purge air cleaning cartridge. 
     Commercial vehicles such as trucks, buses, and large commercial vehicles are typically equipped with a compressed air braking system in which the brakes of the vehicle are actuated by compressed air. An air compressor is operated by the vehicle engine and storage reservoirs maintain a quantity of pressurized air for the brakes and other compressed air uses. Moisture and oil are two attendant problems associated with compressed air systems and are particularly problems that can adversely affect brake system operation. 
     As a result, an air dryer is incorporated into the compressed air system, and likewise an oil filter. The oil filter is able to remove coalesced oil while the air dryer is effective at removing moisture and oil vapor. Typically, the compressed air passes through a porous material to collect or coalesce the oil before the compressed air passes through a desiccant material that adsorbs or removes moisture from the compressed air. The desiccant material is periodically purged of its moisture content by a reverse or purge flow of air from a segregated purge volume through the desiccant material. During normal operation of these pressure swing absorption air dryers, small quantities of water and oil are expelled with the purge air upon each purge cycle. Water that condenses in the air line and is captured by the desiccant and oil present from bypass lubrication in the air compressor cylinders are expelled to atmosphere and the road surface. Oil on a road surface creates a traction hazard during wet weather and is not environmentally favorable. Likewise, since engine oil is used for compressor lubrication, the air dryer purge is an environmental release point for engine oil contaminated with heavy metals. 
     In known air dryer systems, the desiccant is periodically replaced. “Spin-on” type of canisters or cartridges are particularly desirable since they facilitate maintenance and replacement. In this manner, a desiccant canister is easily removed and substituted with a new canister. 
     Accordingly, a need exists for a design that addresses the discharge of oil to the environment, and still maintains the ease of maintenance and does not otherwise adversely impact on the operation of the air dryer assembly. 
     BRIEF SUMMARY OF THE INVENTION 
     A method and apparatus for cleaning purge air from a compressed air system prior to discharging the air to the environment is provided. In one embodiment, the apparatus is an air dryer which includes a housing having an inlet and outlet that communicate with a cavity having a desiccant material therein. A purge reservoir operatively communicates with the desiccant material cavity for receiving a flow of air purging the desiccant material of moisture before it is introduced to atmosphere. In one embodiment, an oil absorbent cartridge is in communication with the purge valve outlet of the air dryer and includes an absorbent material for removing oil from the air purging the desiccant material. 
     Another aspect of the present invention is a method of collecting oil from a flow of air purging the desiccant material of an air dryer. In one embodiment, the method includes purging an air dryer with a purge air flow and separating oil from the purge air flow prior to discharging the purge air flow to atmosphere. An optional additional aspect of the method includes recycling the oil collected in the oil absorbent cartridge that is affixed to the purge valve outlet of the air dyer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of major components of a compressed air system. 
     FIG. 2 is a cross-sectional illustration of an air dryer assembly incorporating an oil absorbent cartridge. 
     FIG. 3 is a cross-sectional illustration of an air dryer assembly incorporating an oil absorbent cartridge wherein the purge valve is in the actuated position. 
     FIG. 4 is a cross-sectional illustration of a different air dryer assembly incorporating the oil absorbent cartridge of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a compressed air system of the type used, for example in a heavy truck brake system. Although the detailed description of this invention describes the invention in specific relation to a compressed air system used in a heavy truck brake system, one skilled in the art should appreciate that the scope of this invention includes compressed air systems used in other vehicles, as well as compressed air systems in general. An air compressor  10  is driven by a vehicle engine (not shown) in a conventional manner. Pressurized air exits the compressor and passes through an air dryer assembly  12 . Moisture, oil and other contaminants are usually removed from the pressurized air before it is stored in reservoirs  14  or distributed to a downstream use, such as air brakes, and bulk offloading equipment, for example, as represented by reference numeral  15 . 
     FIGS. 2-4 illustrate that the air dryer  12  includes a housing  16  secured to a base  17 . More particularly, a cover  18  closes the replacement desiccant canister  20  that includes a generally circumferential wall  22 , end wall  24 , and a second end wall  26 . A desiccant bed  28  includes a beaded desiccant material, a portion of which is illustrated at  30 . The desiccant material  30  removes moisture and may remove oil and other contaminants from the pressurized air. Check valve  38  allows compressed air out of the desiccant bed and into a surrounding purge volume  40  defined between housing  16  and circumferential wall  22 . A perforated plate  42  is disposed in the desiccant bed  28  and spring  44  maintains pressure on the plate so that the desiccant beads are loaded to inhibit relative movement among the beads. As shown in FIG. 4, the end wall  24  may further include a flow restricting orifice  46  that permits restrictive flow of compressed air from the purge volume  40  into the desiccant bed when the pressure in the desiccant bed drops below a predetermined level. 
     Desiccant canister  20  is secured to the housing base plate  17  along wall  22  either by the bolt  47  as shown in FIGS. 2 and 3, a set of corresponding threads  50  and  52  as shown in FIG. 4, or by some other conventional fastening means. In this manner, the desiccant canister can be installed and removed relative to the base by engaging or disengaging the threads  50  and  52  or the bolt  47 . 
     The air dyer assembly  12  may include an oil coalescing element such as the coalescing oil filters  58  or  59  shown in FIGS. 3 and 4 respectively. 
     A supply air inlet port  62  communicates with the air compressor  10 . Delivery port  64 , on the other hand communicates with reservoir  14  and is controlled by check valve  66 . A control port  68  provides a pressure control signal indicative when the compressor goes offload. 
     A purge control valve  70  is slidably mounted within the base  17 . Purge control valve  70  includes an exhaust valve portion  72  that cooperates with exhaust valve seat  74  and an inlet valve portion  78  that cooperates with valve scat  80  to selectively control communication between the supply port  62  and the passage  76 . The purge control valve  70  moves from a first position illustrated in FIG. 2, where the exhaust port  77  is closed and communication is permitted between supply port  62  and passage  76 , to an actuated position, as illustrated in FIG. 3, in which the valve surface  78  closes against valve seat  80  to terminate communication between the supply port  62  and passage  76 . This movement of the purge control valve  70  opens purge air exhaust port  77  to vent the passage  76 . In the past, the purge air exhaust port  77  communicated directly with atmosphere. Additionally, oil vapor traveling through passageway  76  condenses in air reservoir  99 . During the purge cycle of the air dryer  12 , air passes from purge volume  40  through the air dryer and reservoir  99  and carries the condensed oil vapor out through exhaust port  77  to the environment. 
     A purge air cleaner  100  may be added to a conventional air dryer as a new air dyer unit or may be adapted to retrofit existing air dryer assemblies. The purge air cleaner  100  includes a housing  102  having an internal cavity  104 . The cavity is filled with an absorbent material  106 , shown here as a fixed bed of an absorbent material, that retains oil for either safe disposal or solvent extraction. It should be understood that an absorbent material is a material that will absorb, adsorb, retain, entrap, or otherwise remove oil from the purge flow. Preferably, the absorbent material is hydrophobic, such as melt blown polypropylene, for example, for better oil assimilation. A hydrophobic absorbent material will also reject water, thereby enhancing the oil retention capacity of the absorbent. In one embodiment, the material  106  is formed as a porous, fixed bed inside a canister or housing  102 , which is connected to the air dryer purge valve  70 . One skilled in the art will appreciate that other absorbent materials and configurations may be used to remove the oil entrained in the purge air flow. For example, the absorbent material  106  may be a corrugated sheet or a bed of granulated material. Likewise, other engineered shapes that channel air uniformly through the bed and enhance air contact with the absorbent can be used. Thus, purge air flow that would in the prior art have been directed to atmosphere from the purge valve  70  moved to an actuated position, in which the exhaust valve portion  72  is spaced from its associated scat  74 , is directed through the canister  100 . An exhaust opening  120  allows the cleaned purge air to be directed to atmosphere. The path from the purge valve  70  to the port  120  requires the purge air to flow through the absorbent material  106 . Oil is thereby removed from the purge air before being discharged to the environment. 
     An external threaded region  110  is provided on an extending portion of a retaining member  111  associated with the air dryer  12 . Likewise, internal threads  112  are provided on a neck region of the purge air cleaner  100 . In this manner, the purge air cleaner can be easily assembled and removed from the remainder of the air dryer cartridge. The use of a spin-on type arrangement allows the purge air cleaner  100  to be easily removed for inspection, maintenance, or replacement. 
     As will be recognized, a purge air cleaner can be provided as original equipment or, in some instances, can be a retrofit arrangement. In either instance, oil is effectively removed from purge air before being discharged to surrounding environment. By using a spin-on type of cartridge, ease of replacement and substitution with a new cartridge can be attained. The entire canister can be removed and replaced by a new cartridge so that solvent extraction, safe disposal, or recycling of the oil is achieved. 
     It will be appreciated that the purge air cleaner may adopt a wide variety of configurations and be secured to an air dryer in a variety of manners. This invention is intended to include such modifications and alterations in so far as they fall within the scope of the appended claims or the equivalents thereof.