Abstract:
A membrane air dryer includes a proportioning valve for providing sweep air to the dryer. The valve may be located in an easily accessible location and may be oriented so that the movable valve element extends transverse to the length of the shell. The valve may be configured to allow air to flow back from the delivery port to the fibers during a compressor unload cycle to maintain pressure on the fibers, while blocking flow of air from the delivery port to the sweep chamber.

Description:
BACKGROUND  
       [0001]    The present invention relates to a vehicle compressed air system, an air dryer for such a system, and a sweep proportioning valve for such an air dryer. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0002]      FIG. 1  is an illustration of a bore fed membrane air dryer including a sweep valve, which is a first representative embodiment of the invention; 
           [0003]      FIG. 2  is an illustration showing parts of the sweep valve of the first embodiment, in a different condition of operation; and 
           [0004]      FIG. 3  is an illustration of a shell fed membrane air dryer including a sweep valve, which is a second representative embodiment of the invention. 
       
    
    
     DESCRIPTION  
       [0005]    The present invention relates to a vehicle compressed air system, an air dryer for such a system, and a sweep proportioning valve for such an air dryer. The present invention is applicable to various types of air dryers. For example, the invention is applicable to bore-fed membrane air dryers, and to shell-fed membrane air dryers.  FIG. 1  shows a bore-fed membrane air dryer  10  with a sweep valve  12 . The sweep valve  12  of  FIG. 1  is also usable in association with a shell-fed membrane air dryer, as will be described below in more detail.  FIG. 3  shows a shell-fed membrane air dryer  10   a  with a sweep valve  12   a . The sweep valve  12   a  of  FIG. 3  is also usable in association with a bore-fed membrane air dryer, as will be described below in more detail. 
         [0006]    In the embodiment of  FIG. 1 , the dryer  10  includes a shell  20 . In the illustrated embodiment, the shell has an elongate cylindrical configuration centered on an axis  22 . The shell  20  includes an imperforate outer tube  24  and a perforated inner tube  26 . 
         [0007]    A tubular bundle  30  of fibers  32  is supported in the shell  20  between the inner and outer tubes  24  and  26 . Each fiber  32  is a membrane having a bore though which air to be dried can be passed, to remove water from the air. The bundle  30  of fibers  32  forms a membrane assembly in the dryer  10 . At each end of the bundle  30  is an epoxy plug  34  that seals the spaces between the various fibers  32 , to provide a barrier between the high pressure side of the dryer  10  and the low pressure side of the dryer. 
         [0008]    In the approximate center of the inner tube  26  is a stopper or plug  36 , which may be made of an elastomeric material, such as rubber. The stopper  36  impedes or blocks air flow longitudinally through the inner tube  26  and forces air flowing through openings  38  in the inner tube to move radially outward into the bundle  30  of fibers. 
         [0009]    An inlet housing  40  is located at one end of the shell  20 . The inlet housing  40  has a compressor inlet  42  with a check valve shown schematically at  44 . The compressor inlet  42  opens into an inlet chamber  46  that directs compressed air into the bores of the fibers  32 . The inlet housing  40  also has a centrally located sweep air outlet chamber  48 , that opens from the inner tube  26  of the shell  20 . The sweep air outlet chamber  48  has a vent  49  for venting air and water to the atmosphere. 
         [0010]    A sweep valve housing  50  is located at the other end of the shell  20 . The valve housing  50  has a delivery port  52  for directing air out of the dryer  10  to the system including the reservoir. The delivery port  52  opens from an outlet chamber  54  in the valve housing  50 . The valve housing  50  also defines a delivery chamber  56  into which the bores of the fibers  32  in the bundle  30  open. The delivery chamber  56  extends about a sweep air inlet chamber  58  that opens into the inner tube  26  of the shell  20 . 
         [0011]    The sweep valve  12  ( FIG. 2 ) is located in the housing  50 . The sweep valve  12  includes a movable valve element  62  and two fixed valve elements. The fixed valve elements are on the valve housing  50  and include a first valve seat  64  and a second valve seat  66 . The first valve seat  64  extends around an opening  68  in the valve housing  50  that enables air to flow between the delivery chamber  56  and the outlet chamber  52 . The second valve seat  66  extends around an opening  70  in the valve housing  50  that enables air to flow between the delivery chamber  56  and the sweep air inlet chamber  58 . 
         [0012]    The movable valve element  62  includes a needle  80  and a bobbin  100  supported on the needle for movement together with the needle. The needle  80  and bobbin  100  extend, and move, transversely to the longitudinal extent of the dryer. In this embodiment, for example, the needle  80  and bobbin  100  extend, and move, perpendicular to the longitudinal extent of the dryer. 
         [0013]    The needle  80  has a cylindrical configuration. The lower portion  82  of the needle  80 , below the bobbin  100 , is tubular. A flat is machined on one side of the lower portion  82  of the needle  80 , to provide a tapered opening  86  in the lower portion of the needle. This configuration is less expensive to fabricate than, for example, machining a conical end portion of the needle  80 . 
         [0014]    The lower portion  82  of the needle  80  extends through the opening  70  in the valve housing  50  between the delivery chamber  56  and the sweep air inlet chamber  58 . The second valve seat  66  extends around the opening  70  and thus around the lower portion  82  of the needle  80 . 
         [0015]    An O-ring as shown at  88  in  FIG. 2  is smaller than the needle  80  and is stretched onto the needle. Thus, the O-ring  88  moves with the needle  80  as the movable valve element  62  moves. The O-ring  88  is movable between a first position shown in  FIG. 1  resting on and sealing against the second valve seat  66 , and a second position shown in  FIG. 2  spaced apart from the second valve seat and allowing air to flow from the delivery chamber  56  into the sweep air inlet chamber  58 . 
         [0016]    The upper portion  90  of the needle  80 , above the bobbin  100 , is movably supported in a cap  92  that is threaded into the valve housing  50  at an accessible location on the exterior of the end of the dryer  10 . The cap  92  can be unscrewed from the valve housing  50  for easy access to and maintenance of the sweep valve  12 . 
         [0017]    The bobbin  100  may be made from plastic or metal, or from another material. The bobbin  100  extends through the opening  68  in the valve housing  50  between the delivery chamber  56  and the outlet chamber  54 . The first valve seat  64 , which extends around the opening  68 , is engageable by the bobbin  100 . In the particular embodiment shown in  FIG. 1 , this is not a sealing engagement; rather, air can leak past the area of engagement, as discussed below. 
         [0018]    The bobbin  100  has a tapered main body portion  102  that is locatable below the first valve seat  64 . The tapered portion  102  of the bobbin  100  is located at least partially in the delivery chamber  56  at a location between the fiber bundle  30  and the first valve seat  64 . As a result, the tapered portion  102  of the bobbin  100  is exposed to flow of pressurized air flowing from the fiber bundle  30  when the system is being charged. 
         [0019]    When the system is charging, compressed air from the compressor flows through the compressor inlet  42  and into the inlet chamber  46 . The compressed air flows through the bores of the fibers  32  and is dried therein. Water that is removed from the air migrates to the outside of the fibers  32 . 
         [0020]    The dried air from the fibers  32  of the fiber bundle  30  flows into the delivery chamber  56  of the valve housing  50 . The dried air engages the tapered surface  102  of the bobbin  100  and forces the bobbin to move upward as viewed in FIGS. I and  2 . As the bobbin  100  moves upward, it moves off the first valve seat  64 , allowing dried air to flow from the delivery chamber  56  to the outlet chamber  54  and thence through the delivery port  52  to the reservoir. The amount of movement of the bobbin  100  is proportional to the flow of air. 
         [0021]    Also as the bobbin  100  moves upward, it pulls the needle  80  upward. The lower portion  82  of the needle  80  moves in the opening  70 , as the O-ring  88  moves away from the second valve seat  66 . This movement enables dried air to flow from the delivery chamber  56 , through the opening  70 , and into the sweep air inlet chamber  58 . The volume of flow is proportional to the amount of needle movement. Thus, the flow of dried air delivered to the sweep air inlet chamber  58  is proportional to the flow of dried air to the delivery port  52 . This proportionality is in accord with the increased amount of air being dried and moisture being removed. 
         [0022]    The inner tube  26  of the shell  20 , together with the spaces between the several fibers  32 , forms a sweep air chamber  110  of the dryer  10 . The sweep air flows from the sweep air inlet  58  chamber, into the portion of the sweep air chamber  110  that is in the inner tube  26 . The sweep air flows through the perforations  38  in the inner tube  26  to surround the various fibers  32  and pick up moisture from them. The sweep air transports the moisture to the sweep air outlet chamber  48  and then to the vent  49 . 
         [0023]    An elongate dryer, such as the dryer  10 , is typically mounted horizontally in a vehicle, such as a truck, because of space constraints. When the dryer  10  is mounted horizontally, the needle  80  and bobbin  100  extend and move vertically. As a result, the needle  80  and the bobbin  100  can close against their respective valve seats,  64  and  66 , under the influence of gravity. No biasing member, such as a spring, is needed. This can provide a less complex and more reliable sweep valve mechanism. 
         [0024]    In addition, the end mounting of the sweep valve  12  (on the end of the dryer  10 ) provides easy access to the moving parts of the sweep valve. All that needs to be done is for the cap  92  to be unthreaded and the movable valve element  62  to be lifted out. 
         [0025]    Minimizing deep pressure cycling of the fibers  32  can be beneficial to durability of the fibers. Thus, it may be desirable to maintain a continuous pressure within the bores of the fibers  32 , or at least to keep pressure variation over time to a relatively low degree, for example, the 15-20 psi pressure differential between the low and high pressures at which the system governor turns the compressor on and off. 
         [0026]    In the dryer  10  of  FIG. 1 , this is accomplished by providing reservoir pressure to the bores of the fibers  32  when the compressor is not charging. To this end, the bobbin  100  and/or first valve seat  64  of the sweep valve  12  of  FIG. 1  are, as noted above, configured to provide a leakage path to allow some leakage around the bobbin where the bobbin is engageable with the first valve seat. As a result, when the compressor is unloaded and not forcing air into the bores of the fibers  32 , air under pressure from the reservoir can flow back through the delivery port  52 , past the bobbin  100 , and into the bores of the fibers  32 . This air is at reservoir pressure which is typically no more than 15-20 psi less than compressor output, rather than the 100 psi or greater pressure differential between compressor output pressure and ambient pressure. Therefore, the pressure variation in the bores of the fibers  32 , over time, is limited, which can help to increase the durability of the fibers. 
         [0027]    At the same time, it would not be desirable for air flowing back from the reservoir to enter the sweep chamber  110 , because the sweep chamber is vented to atmosphere. Therefore, the sweep valve  12  of  FIG. 1  is configured to provide a tight seal (via the O-ring  88 , for example) at the location of the second valve seat  66 . As a result, when air under pressure from the reservoir is flowing back through the delivery port  52  and past the bobbin  110 , it can not flow past the needle  80  into the sweep chamber  110 . Such flow is prevented by the tight seal of the sweep valve  12 . 
         [0028]      FIG. 3  illustrates a dryer  10   a  that is a second embodiment of the invention. Portions of the dryer  10   a  that are the same as or similar to portions of the dryer  10  are given the same reference numerals with the suffix “a” attached”. In general the differences from the first embodiment are that the dryer  10   a  is a shell-fed dryer, not a bore-fed dryer; and the sweep valve seals at the bobbin and not at the needle. 
         [0029]    The dryer  10   a  ( FIG. 3 ) includes an inlet housing  40   a  that accepts compressed air centrally into an inlet chamber  46   a . The inlet chamber  46   a  opens into the inner tube  26   a  of the shell  20   a . The inlet housing  40   a  also has a sweep air outlet chamber  48   a  that extends around the inlet chamber  46   a . The sweep air outlet chamber  48   a  communicates with the outlet ends of the fiber bundle  30   a  and has a vent  49   a.    
         [0030]    The dryer  10   a  includes a sweep valve housing  50   a  that accepts dried air centrally into a delivery chamber  56   a . The delivery chamber opens into an outlet chamber  54   a  via an opening in the housing  50   a.    
         [0031]    The sweep valve housing  50   a  includes a sweep air inlet chamber  58   a  that extends around the delivery chamber  56   a . The sweep air inlet chamber  58   a  is in fluid communication with the inlet ends of the fibers  32   a  in the bundle  30 . The bores of the fibers  32   a  form a sweep chamber  110   a  of the dryer  10   a . The sweep air inlet chamber  58   a  opens to the delivery chamber  56   a  via an opening in the housing  50   a.    
         [0032]    The movable valve element  62   a  includes a bobbin  100   a  having a tapered main body portion  102   a  disposed at least partially in the delivery chamber  56   a . A lower portion of a needle  80   a  extends into the sweep air inlet chamber  58   a . The lower portion of the needle  80   a  has a tapered opening  86   a.    
         [0033]    When the system is charging, compressed air from the compressor flows through the compressor inlet and into the inlet chamber  46   a . The compressed air flows through the inner tube  26   a  and around the fibers  32   a  of the bundle  30   a . The air is dried by contact with the fiber bundle  30   a . Water that is removed from the air migrates to the bores of the fibers  32   a.    
         [0034]    The dried air from the shell  20   a  flows into the delivery chamber  56   a  of the valve housing  50   a . The dried air engages the tapered surface  102   a  of the bobbin  100   a  and forces the bobbin to move upward. 
         [0035]    As the bobbin  100   a  moves upward, it moves off the first valve seat  64   a , allowing dried air to flow from the delivery chamber  56   a  to the outlet chamber  54   a  and thence through the delivery port  52   a  to the reservoir. The amount of movement of the bobbin  100   a  is proportional to the flow of air. 
         [0036]    Also as the bobbin  100   a  moves upward, it pulls the needle  80   a  upward. The lower portion of the needle  80   a  moves upward away from the second valve  66   a  seat. This movement enables dried air to flow from the delivery chamber  56   a  into the sweep air inlet chamber  58   a . The volume of flow is proportional to the amount of needle movement. Thus, the flow of dried air that is delivered to the sweep air inlet chamber  58   a  is proportional to the flow of dried air to the delivery port  52   a . This proportionality is beneficial because it is in accord with the increased amount of air being dried and moisture being removed. 
         [0037]    The sweep air flows from the sweep air inlet chamber  58   a  into the bores of the fibers  32   a . The sweep air picks up moisture and transports it to the sweep air outlet  48   a  chamber and then to the vent  49   a.    
         [0038]    In the embodiment shown in  FIG. 3 , the bobbin  100   a  makes an air tight seal against backflow of air from the delivery port  52   a , thus acting as a check valve. At the same time, the engagement of the needle  80   a  in the second valve seat  66   a  is configured to provide a leakage path to allow some leakage of air. This would allow a small flow of air from the inner tube  26   a  of the shell  20   a  through the sweep air chamber  58   a  of the dryer  10   a  to atmosphere, effectively opening the compressor output to atmosphere and depressurizing the discharge line from the compressor. This would allow the compressor, when it is loaded, to start against a depressurized line, which may be preferable. Also, the leaky needle valve may exhibit a reduced pull of force, or lift off force. The reduced stiction enables easier movement of the bobbin  100   a  and needle  80   a.    
         [0039]    In addition, allowing back flow of air through the sweep chamber  110   a  (the fiber bores in this embodiment) can provide for additional drying of the fibers  32   a . This can be useful because some fibers dry less effectively at lower pressure differentials, such as are present when the compressor is starting up at the end of a charge cycle. Sweeping the membrane in this manner, to dry it further, can help to compensate for this potentially reduced effectiveness. 
         [0040]    At least two other embodiments are possible. First, a shell-fed dryer can incorporate the sweep valve  12  of  FIGS. 1 and 2 . In this case, air from the reservoir is allowed to return to the dryer chamber, to maintain pressure on the side of the fibers that is pressurized during normal operation of the dryer. The return air would flow into the shell side of the dryer. The seal between the needle and the valve housing would prevent air from the reservoir from flowing into the sweep chamber. 
         [0041]    Second, a bore-fed dryer can incorporate the sweep valve  12   a  of  FIG. 3 . In this case, air from the reservoir is blocked from returning to the dryer, by the seal between the bobbin and the valve housing. At the same time, the leakage path between the needle and the valve housing allows a small flow of air from the inner tube of the shell through the sweep air chamber to atmosphere, effectively opening the compressor output to atmosphere and depressurizing the discharge line from the compressor.