Abstract:
A trailer air dryer is provided to minimize contamination, leakage or freeze-up of the valves used in a pneumatic braking and suspension system caused by moisture or foreign particles in the system. A bypass assembly is provided to ensure normal brake operation should the filters or drying material/desiccant become plugged. In one embodiment, an audible signal or warning is provided to the operator indicating need for servicing the trailer air dryer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an air dryer system for use in a compressed air system. More particularly, the invention relates to an air dryer system for use in a trailer where protection that is normally provided for the tractor may not be available. 
     2. Discussion of the Art 
     Compressed air systems are widely used to operate a number of devices, and find particular use in braking systems for heavy vehicles. These systems include an air compressor which compresses ambient air and charges a storage reservoir. The compressor is engine operated and a governor, responsive to the reservoir pressure, selectively enables or disables the compressor as needed. Air dryers commonly employ a drying material or desiccant through which air passes to remove entrained moisture and limit problems associated with moisture associated with brake system components. Moisture is adsorbed by the desiccant and removed from the compressed air before it is communicated to the storage reservoir. In these known systems, periodic or cyclic purging of the air dryers is required in order to purge or regenerate the desiccant. 
     No provision has been made for trailer air dryers to separately protect devices that may not be protected by the tractor&#39;s air dryer. As will be appreciated, contamination, foreign particles, leakage, and freeze-up of the pneumatic valves used in trailer braking and trailer suspension systems can be associated with the lack of an effective trailer dryer system. Therefore, there is a perceived need for a trailer air dryer that simultaneously filters and dries wet air sent to the trailer. The active drying material can act as a moisture buffer, adsorbing moisture from the air during wet air consumption, and releasing previously captured moisture in vapor phase when the incoming air is dry, thereby regenerating the desiccant in a non-cyclic fashion. 
     SUMMARY OF THE INVENTION 
     The present invention solves the noted problems and others and provides an air dryer useful in a trailer braking and suspension system. 
     According to the invention, an air dryer for a trailer braking assembly includes a housing having first and second passages extending therethrough. Each passage has a drying material disposed therein for removing moisture directed through the passage. A third passage provides a bypass if a predetermined differential pressure threshold is exceeded. 
     According to another aspect of the invention, the first and second passages are different sizes to accommodate the supply and control air, and bypasses are provided for each passage if a predetermined differential pressure threshold is exceeded. 
     According to another aspect of the invention, a filter is associated with the drying material in each passage to clean the air passing therethrough. 
     According to a still further aspect of the invention, a signal generator is associated with the housing to provide a signal to the operator that the differential pressure threshold has been exceeded. 
     A primary benefit of the present invention is the ability to protect devices that may or may not be protected by the tractor. 
     Still another benefit resides in the ease with which the air dryer assembly can be incorporated into the trailer braking system. 
     Yet another benefit of the invention is realized by the ability to effectively remove the air dryer from the trailer braking system if it becomes plugged or blocked. 
     Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal, cross-sectional view of a preferred form of trailer air dryer assembly; 
     FIG. 2 is a cross-sectional view taken generally along the lines  2 — 2  of FIG. 1; 
     FIGS. 3A and 3B are enlarged views of a preferred bypass valve assembly; 
     FIG. 4 is an enlarged cross-sectional view of a delivery side end cover; 
     FIG. 5 is an enlarged cross-sectional view of a supply side end cover; 
     FIG. 6 is a cross-sectional view of an alternative valve bypass valve structure; and 
     FIG. 7 is a graphical representation comparing time relative to humidity in accordance with the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 are cross-sectional views of a first preferred embodiment of the trailer air dryer  10 . The air dryer includes a housing  12  which is preferably an aluminum extrusion that is simple and cost effective to manufacture. Of course, alternative constructions are also contemplated without departing from the scope and intent of the present invention. The housing includes a series of generally parallel passages extending therethrough. A first passage or supply passage  14  has the largest cross-sectional dimension of all the passages and is adapted to provide supply air used for trailer braking. A second, or control line, passage  16  is of slightly smaller cross-sectional dimension and is intended to carry a control signal or pneumatic pressure signal to actuate the valve in response to operator demand. The supply and control line passages each include a drying material such as a desiccant material  18  or other drying agent. The drying material fills the entire cross-section of the passage and extends for a majority of the longitudinal extent of each of the passages. The drying material is preferably contained at opposite ends by filter members  30 . For example, a preferred filter member is a perforated cloth and filter media that removes particles from the air flow through the supply and control line passages. The drying materials and filter members are axially held in place in the passages by end covers  32 ,  34 , details of which will be described further below. End cover seals  36 ,  38  are interposed between the housing and end covers to provide a sealed arrangement. As will be appreciated, any conventional type of seal assembly can be used. 
     In addition, a biasing assembly is provided to maintain a desired preload and compaction of the drying material. In the preferred arrangement, the biasing assembly is defined by a pair of springs  40 ,  42  received at one end of the passages  14 ,  16 , respectively. The springs are illustrated as coil springs that engage the end cover  32  at one end and the associated filter member at the other end. The springs impose a slight compressive force or compaction on the drying material so that it operates in its intended manner. 
     Each end cover includes passages that communicate with the supply line and the control line (not shown), respectively. For purposes of identification, these passages are identified as  50 ,  52  in the supply side of the end cover and  54 ,  56  in the delivery side end cover. During normal operation of the trailer air dryer, air flow proceeds into the opening  50 , through the filters and drying material in passage  14 , and exits via the passage  54  in the second end cover. Likewise, the pneumatic control signal is sent through opening  52 , through the filter members and drying material of passage  16 , and outlets through opening  56  in the second end cover. 
     Since the trailer air dryer assembly is inserted in the lines or hoses that communicate with the brakes of the trailer, any failure mode could potentially result in a no brake situation. Therefore, it is important to have a bypass arrangement that assures normal operation of the braking and would temporarily remove the dryer assembly from the trailer braking assembly if a failure mode is encountered. For example, if the filters or desiccant material becomes plugged, it is desirable to have a relief or bypass arrangement that operates at a low pressure differential (i.e, a few psi pressure differential) to open. FIG. 2 illustrates bypass passages  60 ,  62  that are parallel to the passages  14 ,  16  through the housing. In the preferred arrangement, one of the bypass passages is controlled by a supply side bypass valve located in one of the end covers here, the first or supply side end cover  32 . Each of the bypass valves is of similar construction and each allows flow in either direction in response to a pressure differential. Accordingly, if pneumatic flow through the supply passage  14  is blocked or plugged, the supply bypass valve in the end cover  32  opens and allows air from the inlet  50  to reach the bypass passage  62 . Air then proceeds through the bypass passage to the second end cover  34  and ultimately supplies air to the trailer braking system. Likewise, if flow through the control passage  16  is blocked, the relief valve in the end cover  32  opens, thereby allowing air from inlet  52  to communicate through bypass passage  60  with the outlet  56 . As mentioned above, if either the supply or control passage is blocked, the relief valves are designed to allow flow in the opposite direction through the bypass passages also. Thus, a small pressure differential, on the order of a few psi, is sufficient to open either of the bypass valves. 
     Turning now to FIGS. 3A and 3B, a preferred form of bypass valve is shown as a reed valve  70 . A pair of plates or disks  72   a,    72   b  are of identical construction and secured together, such as by spot welding the metal disks together. An opening  74   a,    74   b  and key-holed shaped slot  76   a,    76   b  are provided in each disk. The slot forms a reed valve member  78   a,    78   b,  that is integrally connected with the remainder of the disk via a narrow dimension, flexible arm  78   c,    78   d.  The valve member  78  is larger than the opening so that when the disks are secured in facing, mating relation, the valve member of one disk overlies the opening in the other disk. A keyed arrangement, such as notches in the periphery of the disk, may be provided to properly orient the disks relative to one another and also orient the assembly in the end cover. Moreover, the forming operation of the valve member imposes a preload so that the valve member seats or seals about the periphery of the opening and the arm flexes the valve member to an open position in response to a small pressure differential on the order of a few psi. Thus, flow in either direction is provided through the valve assembly. 
     FIGS. 4 and 5 illustrate a second preferred embodiment. Where convenient, like numerals will be used to identify like components and new components are identified by new numerals. For example, in FIG. 4, if air from the supply inlet port  50  cannot pass through passage  14 , the pressure differential opens a diaphragm bypass valve represented by numeral  80 . This establishes communication with cavity  82  on the first or upper side of diaphragm  84 . A biasing force is imposed by spring  86  urging the diaphragm toward a seated condition. When the supply passage  14  is blocked, the biasing force of the spring is overcome and air flow proceeds past valve seat  88  for communication with the supply bypass tube  62 . Similarly, air returning through the supply bypass tube will act on a second face, or underside, of the diaphragm  84  to lift it from associated seat  90  and allow air to exit via passage  92 . To lift the diaphragm from the seat  90  requires the biasing or closing force of spring  94  to be overcome. 
     The supply bypass valve  80  has the added feature of providing an audible signal to the operator indicating use of the bypass passage. That is, the diaphragm valve assembly is configured so that air flow past the diaphragm  84  and seat  90  to the outlet  92  provides an audible “honk”. This alerts the operator that the bypass passage is in use and of the need for service since communication through the desiccant bed of supply passage  14  is not functional. 
     FIG. 5 illustrates a similar valve structure in the delivery side end cover. In the preferred embodiment, the delivery side end cover  34  houses the control bypass valve  100 . It, too, is a diaphragm valve as shown in this particular illustration. Particularly, air from the control bypass tube  60  communicates with cavity  102  disposed on a first or upper side of the diaphragm member  104 . The diaphragm is normally urged by spring  106  into engagement with the valve seat  108 . Accordingly, a sufficient buildup of pressure on the upper face of the diaphragm will overcome the force of the spring and allow communication between the control bypass passage and the control port through a passage  110 . Similarly, reverse flow through the control port  56  also acts on the second or underside  112  of the diaphragm, thus overcoming the closing force imposed by spring  114  urging the diaphragm against the seat  116 . 
     FIG. 6 illustrates yet another preferred form of bypass valve assembly. It discloses a single, annular steel diaphragm that has a predetermined bow or contour seating against a radially inner seat  122  and a radially outer seat  124 . In much the same manner as described above, this diaphragm arrangement, without the need for additional springs to preload or bias the diaphragm in opposite directions, is responsive to a small psi differential pressure to open in either direction. 
     It will be appreciated that the embodiments of FIGS. 3 and 6 are simpler from a manufacture and assembly standpoint. On the other hand, the embodiment of FIGS. 4 and 5 includes the ability to provide an audible signal to the operator indicating a blocked supply or control passage. It will also be recognized with regard to the embodiment of FIGS. 4 and 5 that only one of the bypass valve assemblies incorporates the audible signal feature. That is, the air flow through the delivery side end cover is used for applying the brakes so that the valve will not provide an audible signal resulting from flow in that direction. It is only during reverse flow, i.e., the release direction, that the audible signal is available. 
     FIG. 7 provides a graphical representation of the operation of the air dryer as a moisture buffer. As humidity changes over time, and the air proceeds through the air dryer, there are occasions as represented by curve portion  130  where moisture in the input air  130  is removed as represented by the output  132 . At other times during operation, the moisture content in the air is below the predetermined output as represented by curve portion  130   b.  Thus, some of the moisture entrained in the drying material is released to the dry air and removed from the assembly. In this manner, the moisture level can be controlled downstream of the trailer air dryer so that operation of the valves or other components of the truck braking system are not adversely effected. By moderating the amount of moisture that the actuating components encounter, damage is minimized that would otherwise lead to potential freeze-up or other general moisture problems. 
     In addition, this assembly is intended for one-time use, i.e., it is not designed to be a service device or one in which spare parts are sold. Remanufacture is contemplated upon return of the device to the OEM. It is for these additional reasons that a simple, inexpensive air dryer arrangement is desired that can be easily inserted and removed into a trailer braking system. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon a reading and understanding of the detailed description. The invention is intended to include such modifications and alterations in so far as they come within the scope of the appended claims and equivalents thereof.