Abstract:
A method and apparatus for mounting an air dryer to a commercial vehicle is provided. The end caps of the membrane air dryer are used to retain the membrane air dryer core and attach the membrane air dryer to the surface of the air supply reservoir. Bosses can be welded to the external surface of the air supply reservoir, which can then be used to mount the membrane air dryer by bolting the end caps to the bosses. The method and apparatus can be applied to two or three tank air supply reservoir systems. A disengagement tank may be included within the air dryer system, in place of a coalescing filter, to reduce the amount of moisture that reaches the membrane air dryer core.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to an air dryer assembly for a compressed air system, such as, for example, a compressed air braking system for commercial vehicles, and more specifically to a membrane air dryer and method and apparatus for mounting a membrane dryer. 
   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 to effectively remove moisture from the system. Typically, an air dryer contains a desiccant material that adsorbs moisture from the compressed air from the compressor. However, desiccant dryers become saturated, and as a result, require a purge cycle. During the purge cycle, the compressor does not supply compressed air to the system and a backflow of air purges the desiccant material of its moisture content. 
   Membrane air dryers have been used to provide a continuous flow of compressed air to the system. Membrane air dryers allow for a continuous flow of compressed air through a packet of small, hollow tubes within a tubular membrane dryer housing. The hollow fibers are typically a porous plastic material that are coated with a special material that causes the tubes to be permeable to water vapor, but not air. Thus, as air is passed through the membrane dryer hollow fibers, water vapor permeates the fiber walls and collects on the outside of the hollow fibers. Meanwhile, dry air is permitted to pass through to the rest of the system. In order to avoid the accumulation of water vapor on the outside of the fibers, thereby saturating the system, a portion of the dried air is permitted to pass back through the membrane air dryer, this time on the outside of the fibers. The backflow of air is allowed to expand, pickup the water vapor on the outside of the tubes, and then exit the membrane air dryer, typically to atmosphere. Furthermore, since oil vapors, liquid water, carbonous materials, and other contaminants reduce the effectiveness of the membrane air dryer, a filter is typically provided upstream of the membrane air dryer. 
   While membrane air dryers have been established as competitive technology to desiccant dryers in plants and laboratories, membrane air dryers have not been notably implemented on vehicles for compressed air systems partially due to the difficulty in mounting the membrane air dryers to the vehicle. In the past, membrane air dryers have been incorporated into the main air reservoir of the air brake system. However, such mounting configurations do not provide easy access to the membrane air dryer for regular maintenance, inspection, repair or replacement. 
   Furthermore, typical mounting structures for membrane air dryers require a separate set of mounting brackets for securing the membrane air dryer to a vehicle. 
   Accordingly, a need exists for a membrane air dryer design that can be effectively and efficiently mounted to a vehicle in a location that provides relatively easy access for maintenance, inspection, repair or replacement. 
   BRIEF SUMMARY OF THE INVENTION 
   A method and apparatus for mounting a membrane air dryer is provided. One aspect of the present invention is a method and apparatus for mounting a membrane air dryer to a vehicle. In one embodiment, the end caps of the membrane air dryer are attached to the air supply reservoir of a commercial vehicle. In order to mount the membrane air dryer, bosses can be welded to the external surface of the reservoir to provide a means for engaging the membrane air dryer end caps. 
   Another embodiment of the present invention incorporates a disengagement tank into the air dryer assembly. The disengagement tank can be incorporated into the air supply reservoir and provide an outlet that leads to the membrane air dryer core. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a membrane air dryer and mounting end caps of the present invention. 
       FIG. 2  is a close-up view of the supply end cap of a membrane air dryer. 
       FIG. 3  is a close-up view of the delivery end cap of a membrane air dryer. 
       FIG. 4  is a side view of an embodiment of a membrane air dryer incorporating a disengagement tank into the bulkhead of the primary air supply tank. 
       FIG. 5  is a close-up view of the supply end cap of the membrane air dryer of FIG.  4 . 
       FIG. 6  is a membrane air dryer and mounting end caps mounted to a three tank air reservoir system. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates the air dryer system of the present invention, generally referenced as  10 , which includes a membrane air dryer core  20 , a supply end cap  30 , a delivery end cap  40 , and an air reservoir including a primary air supply tank  50 , and a wet tank  60 . The air dryer system  10  optionally includes a coalescing filter  70 , located upstream from the membrane air dryer core  20  to filter out oil vapor, liquid water, carbonous material, and other contaminants. It should be appreciated by one skilled in the art that the coalescing filter  70  may be a variety of types of filters and may have various configurations. For example, the coalescing filter  70  shown in  FIG. 1  is a Bendix PuraGuard filter coupled with a Bendix DV-2 pressure swing drain valve  80 . 
   Compressed air from the compressor is typically saturated with oil vapor, and contains aerosol oil, oil, water vapor, liquid water, carbonous material, and other contaminants. The compressed air is delivered to the coalescing filter  70 , which separates out the heavier contaminants, such as the oil, oil vapor and liquid water. Such contaminants flow to the bottom of the coalescing filter  70 , typically by gravity, where the contaminants are collected until discharged through the drain valve  80 . The compressed air is then fed into the membrane air dryer core  20 , through air inlet  90  located in the supply end cap  30 . The compressed air is then fed through the membrane air dryer core  20  wherein water vapor is separated from the compressed air. 
   Since the membrane air dryer core  20  operates in a conventional manner and can take on a number of shapes and configurations, the details of the operation of the membrane air dryer have been omitted from this disclosure. However, since the preferred mounting position for the air dryer is adjacent to the air supply reservoirs, the membrane air dryer may be tubular with a 1-3 inch diameter and 18 to 36 inches long. These numbers are intended to be exemplary in nature and should not be construed in a limiting sense. 
   The compressed air, after traveling through the plurality of membrane air dryer hollow fibers, is now dry and collected in the delivery volume  94  located in the delivery end cap  40 . The dried compressed air in the delivery volume  94  is either fed through the membrane air dryer core  20  as backflow, or through a delivery check valve  96  to the air supply tanks  50  and  60 . The backflow travels along the outside of the membrane air dryer fibers, collects the water vapor and vents to the atmosphere through vent holes  99 . Air that passes through the delivery check valve  96  passes through the wet tank delivery port  100  and into the wet tank  60 , which is connected to the primary air supply tank by check valve  101 . Air can then be delivered to the rest of the system through air delivery ports  102   a  and  102   b.    
   Now referring to  FIG. 2 , the supply end cap  30  is made from any suitable material, including cast aluminum, and is dimensioned to receive the supply side  103  of the membrane air dryer core  20  in a firm fitting fashion along the inner side wall  104  and end wall  105  of the supply end cap  30 . Air from the filter enters the supply end cap  30  from the air supply line  106  through air inlet  90 . The compressed air then passes to supply volume  108  prior to entering the membrane air dryer fibers. The compressed air is retained within the supply volume  108  by seal  110  located in a recess  112  in the inner wall  104  of the supply end cap  30 . The supply end cap  30  further includes an extended skirt  116  that extends across the length of the membrane air dryer core  20  covering vent holes  99 , thereby protecting the vent holes from dirt and debris. However, in order to enable air and water to escape the vent holes  99 , the extended skirt  116  is raised from the surface of the membrane air dryer core  20 . 
   Supply end cap  30  is mounted to the surface of the primary air supply tank  50 . In one embodiment, as shown in  FIG. 2 , the supply end cap  30  includes an extended brace portion  120  that rests along the contour of the primary air supply tank  50 . A cutout portion  122  of the brace portion  120  receives a boss  125 , which is welded to the primary air supply tank  50 . A bolt  127  can then be threaded through a hole in the brace portion  120  and received within a mating set of threads within the boss  125 . In other embodiments, additional bolts are used to further the supply end cap  30  to the primary air supply tank  50 . Furthermore, in another embodiment, one or more bolts secure the end cap in a forward region of the end cap. Moving the bolts forward helps to alleviate the torque produced by the compressed air entering the membrane air dryer core  20 . In another embodiment, a gusset  129  is added to the supply end cap  30  to provide additional support. 
     FIG. 3  illustrates the delivery end cap  40 . The delivery end cap  40  is made from any suitable material, including cast aluminum, and is dimensioned to receive the delivery side  130  of the membrane air dryer core  20  in a firm fitting fashion along the inner side wall  132  and end wall  133  of the delivery end cap  40 . Dried compressed air enters the delivery end cap  40  from the membrane air dryer core  20  into the delivery volume  94 . The compressed air is retained within the delivery volume  94  by seal  135  located in a recess  137  in the inner wall  132  of the delivery end cap  40 . In one embodiment, the delivery end cap  40  contains a short skirt  139 ; however, in other embodiments, the skirt  139  may be elongated (like the supply side) in order to assist in the retention of the membrane air dryer core  20 . The dried compressed air in the delivery volume  94  either reenters the membrane air dryer core  20  as backflow for collecting and venting the water vapor, or is delivered to the wet tank  60  through the delivery check valve  96  and wet tank delivery port  100 . Face seal  141  can be added to a recess  143  in the bottom of the delivery end cap  40  around the wet tank delivery port  100  to provide an air tight seal. 
   Delivery end cap  40  is mounted to the surface of the wet tank  60 . In one embodiment, the delivery end cap  40  is attached to the wet tank  60  in a similar manner that the supply end cap  30  is attached to the primary air supply tank  50 . In other embodiments, different fastening means are employed to secure the delivery end cap  40  to the wet tank  60 . 
     FIG. 4  illustrates another embodiment of the present invention wherein a disengagement tank  150  is employed to collect and vent water vapor. Compressed air from the compressor and air filter enters the membrane air dryer assembly  10 ′ through inlet  152  in the disengagement tank  150 . The disengagement tank  150  is created by extending the primary air supply tank  50  and adding a bulkhead  154  to separate the two tanks. As the compressed air enters the disengagement tank  150 , it slows and cools thereby allowing water to condense and fall to the bottom of the tank. A drain valve  80  can be added to the bottom of the disengagement tank  150  to vent the condensed water vapor. As shown in  FIG. 5 , air from the disengagement tank  150  enters the supply volume  108  through disengagement outlet port  155 . Face seal  161  can be added to a recess  163  in the bottom of the supply end cap  30  around disengagement tank outlet poll  155  to provide an air tight seal. The remaining aspects of the membrane air dryer assembly  10 ′ are similar to membrane air dryer assembly  10 . 
     FIG. 6  illustrates a third embodiment of the membrane air dryer assembly  10 ″ of the present invention, wherein a three tank reservoir system is employed. As with the other embodiments, dry compressed air enters the wet tank  60  though delivery check valve  96  and wet tank inlet  100 . Once in the wet tank  60 , the air can pass to the primary air supply tank  50  through check valve  101  or to secondary air supply tank  170  through check valve  171 . Air can then be delivered to the remaining components of the compressed air system through air ports  102   a  and  102   b.    
   Although the Figures show the air supply reservoirs as one unit separated by bulk heads, either as a two tank system or three tank system, one skilled in the art should appreciate that the tanks may be separate units. Furthermore, additional tanks may be used or the mounting to the tanks can be done is a different arrangement. One skilled in the art should appreciate that these modifications are within the scope of this application. 
   The present invention also encompasses a method of mounting a membrane air dryer to a vehicle. Since the membrane air dryer has a matching shape as the air supply reservoir, and since the membrane air dryer discharges to the air supply reservoir, it is advantageous to mount the membrane air dryer adjacent to the air supply reservoir. Bosses  125  are welded to the air supply reservoir tank, or tanks, at a predetermined distance depending on the length of the membrane air dryer. The membrane dryer end caps  30  and  40 , with the membrane air dryer core  20  therebetween, are then secured directly to the bosses  135  by one or more bolts  127 . The delivery end cap  40  is aligned such that the delivery check valve  96  connects to the wet tank inlet port  100 . 
   It will be appreciated that the membrane air dryer assembly can take the form of various configurations and mounting arrangements. It should be further understood that the membrane air dryer and corresponding end caps can be used either with new equipment, or retrofit to attach to existing components. Such existing components may cause minor alterations to the design of the membrane air dryer; however one skilled in the art should appreciate that these minor modifications fall within the scope of this application. 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.