Abstract:
A brake cylinder maintaining system that combines a brake cylinder maintaining check valve and a quick service limiting valve into a single unit to have lower hysteresis, and thus more precise BCM regulation pressure and a smaller pressure offset. The check valve and quick service valve are coupled to provide a single system having multiple valve seats for selective communication between quick service pressure and brake cylinder pressure on one hand, and between a brake cylinder maintaining pressure and brake cylinder pressure on the other hand.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to brake cylinder maintaining systems and, more particularly, to a combined brake cylinder maintaining check valve and quick service limiting valve. 
         [0003]    2. Description of the Related Art 
         [0004]    Control valves are used in freight car braking systems to supply air pressure to the brake cylinders of a freight car. If the plumbing between the control valve and the freight car has a leak or there is a leak in the brake cylinder itself, however, then the brake cylinder will not maintain the original set pressure. One approach for addressing this problem is to have a valve that maintains the brake cylinder pressure. When the pressure in the brake cylinder drops below its original set pressure, a brake cylinder maintaining valve may feed brake pipe pressure through a choke to replenish and maintain the brake cylinder pressure up to a designed point. For example, one conventional brake cylinder maintaining (BCM) system for the service portion of a AAR-type control valve includes a BCM charging check valve to reduce brake cylinder pressure by an amount equal to the quick service limiting valve (8-12 psi) plus an amount equal to the sum of the hysteresis, part to part variations, and environmental variations, so that the resulting brake cylinder reference pressure acting on the BCM control side of the diaphragm of the quick service limiting valve plus the quick service limiting valve spring setting (8-12 psi) will always be less than the target/actual brake cylinder pressure. 
         [0005]    Because of the aforementioned sources of variation, it is necessary to set the BCM charging check valve cracking value at 16 to 18 psi. This results in an undesired loss of efficiency of BCM pressure regulation, as the actual brake cylinder pressure would have to leak an amount equal to or greater than the 4-10 psi offset of the BCM charging check before the BCM valve will open to replenish brake cylinder pressure. As a result, a more precise BCM regulation pressure is needed, with a smaller pressure offset, for more accurate and improved brake cylinder maintaining. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention comprises a brake cylinder maintaining (BCM) system having low hysteresis, thereby providing for more precise BCM regulation pressure and smaller pressure offset. The system includes a BCM charging check valve that is integrated into a quick service limiting valve (QSLV) valve. By combining these functions, significant sources of part to part and environmental variations are eliminated and more precise control of the BCM valve is possible. The combined quick service check valve and brake cylinder maintaining valve has a first seat for selectively allowing communication between a brake cylinder pressure chamber and a brake cylinder maintaining pressure chamber and a second seat for selecting allowing communication between the brake cylinder pressure chamber and a quick service pressure chamber. The first seat is normally closed and opens in response to a first predetermined amount of pressurization of the brake cylinder pressure chamber and the second seat is normally open and closes in response to a second predetermined amount of pressurization of the brake cylinder pressure chamber. A diaphragm separates the brake cylinder maintaining pressure chamber and the brake cylinder pressure chamber so that compression of the diaphragm toward the brake cylinder maintaining pressure chamber closes the second seat to prevent communication between the brake cylinder pressure chamber and the quick service pressure chamber. If there is additional compression of the diaphragm toward the brake cylinder maintaining pressure chamber opens the first seat to allow communication between the brake cylinder pressure chamber and the brake cylinder maintaining pressure chamber. The diaphragm is biased from the brake cylinder maintaining pressure chamber toward the brake cylinder pressure chamber so that the first seat is closed and the second seat is open when the pressure in the brake cylinder pressure chamber is less than the first predetermined amount. Preferably, the first predetermined amount is about 10 psi. 
         [0007]    A first embodiment of the invention comprises a valve having a needle passing through the diaphragm and having a channel therethrough that is in communication with the brake cylinder maintaining pressure chamber at one end and is open on the opposing end. The valve further includes a check positioned in the quick service pressure chamber that is biased toward the needle to close the open end of the channel of the needle. Movement of the diaphragm and needle toward the brake cylinder maintaining pressure chamber allows the check to move and close the second seat, thereby preventing communication between the brake cylinder pressure chamber and the quick service pressure chamber. Further movement of the diaphragm toward the brake cylinder maintaining pressure chamber will separate the open end of the channel of the needle from the check and bring the open end of the channel into communication with the brake cylinder pressure chamber, thereby opening the first seat and allowing communication between the brake cylinder pressure chamber and the brake cylinder maintaining pressure chamber. 
         [0008]    In another embodiment of the invention, the valve includes a first stem passing through the diaphragm and defining a passageway between the brake cylinder maintaining pressure chamber and the brake cylinder pressure chamber and a valve head positioned on an end of the valve stem for movement into and out of engagement with the diaphragm, thereby closing or opening the passageway, respectively. A second stem having a post associated with the first stem that extends through the brake cylinder pressure chamber into the quick service pressure chamber. A check is positioned in the quick service pressure chamber and biased toward the post of the second stem so that the check may close the second seat, thereby closing communication between the brake cylinder pressure chamber and the quick service pressure chamber, when the post moves a predetermined distance toward the brake cylinder maintaining pressure chamber. If the diaphragm moves further, the valve head separates from the diaphragm, thereby opening the first seat and allowing communication between the brake cylinder pressure chamber and the brake cylinder maintaining pressure chamber. 
         [0009]    In yet another embodiment of the invention, the valve includes a guide positioned in the diaphragm and a stem having a taper passing through the guide to define a passageway between the brake cylinder maintaining pressure chamber and the brake cylinder pressure chamber. An O-ring engages the taper of the valve step and closing the passageway when the first seat is closed. 
         [0010]    In a further embodiment of the invention, the valve includes a diaphragm having a hole formed therethrough that is sealingly engaged by an end of a valve stem positioned in the brake cylinder pressure chamber for selective opening and closing of the hole in the diaphragm. The opposing end of the valve stem engages a check positioned in the quick service pressure chamber and biased toward the valve stem so that the check may close the second seat when the stem moves a predetermined distance toward the brake cylinder maintaining pressure chamber. The valve stem is biased toward the diaphragm by a spring positioned in the brake cylinder pressure chamber. 
         [0011]    In an additional embodiment of the invention, the valve includes a first stem engaged with one side of the diaphragm and extending through the brake cylinder maintaining pressure chamber into a portion of the brake cylinder pressure chamber to define a passageway therebetween, wherein the first stem engages a check that is biased to close the passageway if the stem is moved out of the portion of the brake cylinder pressure chamber. The valve also includes a second stem engaged with the opposing side of the diaphragm and extending through a second portion of the brake cylinder pressure into the quick service pressure chamber to define a second passageway extending between the brake cylinder pressure chamber and the quick service pressure chamber, wherein the second stem engages a second check that is biased to close the second passageway if the second stem is moved out of the quick service pressure chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0012]    The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a cross-sectional view of a first embodiment of a combined BCM reference pressure charging check valve and quick service limiting valve according to the present invention; 
           [0014]      FIG. 2  is a cross-sectional view of a second embodiment of a combined BCM reference pressure charging check valve and quick service limiting valve according to the present invention; 
           [0015]      FIG. 3  is a cross-sectional view of a third embodiment of a combined BCM reference pressure charging check valve and quick service limiting valve according to the present invention; 
           [0016]      FIG. 4  is a cross-sectional view of a fourth embodiment of a combined BCM reference pressure charging check valve and quick service limiting valve according to the present invention; 
           [0017]      FIG. 5  is a cross-sectional view of a fifth embodiment of a combined BCM reference pressure charging check valve and quick service limiting valve according to the present invention; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Referring now to the drawings, wherein like reference numerals refer to like parts throughout, there is seen in  FIG. 1  a first embodiment of a brake cylinder maintaining valve  10  that integrates a quick service limiting valve and a BCM reference pressure charging check valve into a single unitary structure that cooperates to provide all of the relevant functions with more precise control that otherwise possible. Valve  10  comprises a check valve assembly  12  having a nozzle  14  with a channel  16  formed therethrough that is attached to and extends through a quick service limiting valve (QSLV) diaphragm  18 . Nozzle  14  extends along a longitudinal axis through a brake cylinder pressure chamber  20  in an upper portion of a bushing  22  and through a narrow passageway  24  that separates brake cylinder pressure chamber  20  from a quick service pressure chamber  26  defined in a lower portion of bushing  22 . It should be recognized that the various chambers are in communication with the corresponding elements of a conventional braking system such that the pressure in a particular chamber reflects the pressure in the corresponding element of the braking system. For example, brake cylinder pressure chamber  20  is in open communication with a brake cylinder (not shown) so that the pressure in chamber  20  reflects the pressure in the brake cylinder. 
         [0019]    Nozzle  14  extends through brake cylinder pressure chamber  20  and into quick service pressure chamber  26  to define a first seat A, which selectively controls communication between a BCM reference pressure chamber  28  positioned above QSLV diaphragm  18  and brake cylinder pressure chamber  20 , as well as a second seat B, which selectively controls communication between quick service pressure chamber  26  and brake cylinder pressure chamber  20 . Seat A is formed between the end of nozzle  14  and a check  30  positioned in quick service pressure chamber  26  so that check  30  is in contact with the end of nozzle  14 , seat A will be closed to seal off channel  16 . A second seat B is formed by a clearance gap  32  between the outer surface of nozzle  14  and the interior of passageway  24 . 
         [0020]    A QSLV spring  34  is positioned in a spring guide  36  and configured to bias QSLV diaphragm  18  and nozzle  14  downwardly so check valve  12  is closed at seat A and open at seat B when the pressure in brake cylinder pressure chamber  20  is less than a nominal amount, such as 10 psi. By contrast, check  30  in quick service pressure chamber  26  is biased longitudinally upward by a spring  38  to maintain engagement with the end of nozzle  14  until nozzle  14  withdraws from quick service pressure chamber  26  and check  30  is biased upwardly into engagement with a bead seat  40  surrounding the lower end of passageway  24 , thereby closing seat B. As nozzle  14  continues to withdraw into brake cylinder pressure chamber  20 , and thus away from bead seat  40  and the stationary check  30 , seat A is opened to allow communication between brake cylinder pressure chamber  20  and BCM reference pressure chamber  28  via channel  16  in nozzle  14 . 
         [0021]    In a brake application, after preliminary quick service, quick service pressure chamber  26  will be pressurized by brake pipe pressure as in a conventional braking system. In valve  10 , however, the brake pipe pressure in quick service pressure chamber  26  will flow through open seat B, thereby pressurizing brake cylinder pressure chamber  20  on the underside of QSLV diaphragm  18  and thus pressurizing the brake cylinder which is in open communication with brake cylinder pressure chamber  20 . When brake cylinder pressure chamber  20  under QSLV diaphragm  18  reaches a predetermined amount, such as approximately 10 psi, diaphragm  18  and nozzle  14  move upward. Check  30  will then be biased upwardly by spring  38  and will close against bead seat  40  while nozzle  14  continues to move upward, thereby severing the communication between brake pipe pressure in quick service pressure chamber  26  and brake cylinder pressure chamber  20  (and thus the brake cylinder). As brake cylinder pressure increases further, diaphragm  18  and nozzle  14  will continue to move upward so that nozzle  14  enters brake cylinder pressure chamber  28 , while seat B remains closed and check  30  is stopped in the closed position by bead seat  40 , thereby allowing nozzle  14  to disengage from check  30  and move into brake cylinder pressure chamber  20  while seat A opens. When seat A opens, brake cylinder pressure in brake cylinder pressure chamber  20  can then flow through nozzle  14  to the top side of QSLV diaphragm  18 . Seat A closes when the sum of the pressure in BCM reference pressure chamber  28  acting over the upper area of diaphragm  18  plus the force provided by QSLV spring  34  is equal to or greater than the pressure in brake cylinder pressure chamber  20  acting on the underside of diaphragm  18 . As a result, BCM reference pressure  28  is almost precisely the amount required for a zero-loss BCM function. 
         [0022]    In a brakes applied position, QSLV diaphragm  18  goes to a lap state, where both seat A and seat B are closed. If there is a leak leading to the loss of pressure in the brake cylinder, the pressure in brake cylinder pressure chamber  20  on the underside of QSLV diaphragm  18  will be reduced and diaphragm  18  will move nozzle  14  downward, thereby pushing check  30  against the bias of spring  38  and opening seat B. As a result, brake pipe pressure may flow from quick service pressure chamber  26  through open seat B to the brake cylinder via brake cylinder pressure chamber  20  until a pressure balance is restored across QSLV diaphragm  18 . 
         [0023]    Additional embodiments, such as the second, third, fourth and fifth embodiments discussed below, may be structured to add a predefined amount of hysteresis or pressure offset to the BCM reference pressure to provide added valve stability. For example, in a second embodiment of a combined quick service check valve and brake cylinder maintaining valve  50 , a normally closed check valve  52  is integrated into a QSLV diaphragm  54  under a valve cover  56 . Check valve  52  includes a first valve stem  58  that passes through a valve guide  60  positioned in an opening  62  in QSLV diaphragm  54 . A valve head  64  positioned on the lower side of QSLV diaphragm  54  defines a first seat A between the edge of valve head  64  and the lower side of QSLV diaphragm  54 . Seat A allows for selective communication between a brake cylinder pressure chamber  66  positioned below QSLV diaphragm  54  and a BCM reference pressure chamber  68  positioned above QSLV diaphragm  52  via a clearance gap  70  between valve guide  60  and valve stem  58 . QSLV diaphragm  52  is biased downwardly by a QSLV spring  72  positioned in a spring guide  74  so that seat A is normally closed. First valve stem  58  is also biased by a spring  76  that engages a retaining ring  78  positioned at the upper end of valve stem  58  to hold valve head  64  into engagement with QSLV diaphragm  52 . As explained below, however, valve head  64  will separate from QSLV diaphragm  52  if first valve stem  58  moves upwardly distance D into contact with valve cover  56 . 
         [0024]    As further seen in  FIG. 2 , first valve stem  58  cooperates with a second valve stem  80  that is positioned in brake cylinder pressure chamber  60  and that includes a post  82  extending through an passageway  84  into a quick service pressure chamber  86 . Post  82  is moveable into engagement with a check  88  to define a second seat B. Check  88  is biased upwardly against post  82  by a spring  90  and can move through a distance C before engaging a bead seat  92  and closing off passageway  84 . Post  92  does not completely occupy passageway  84 , thereby allowing for communication between quick service pressure chamber  86  and brake cylinder pressure chamber  66  when check  88  has not closed passageway  84 . Second seat B therefore allows for selective opening of communication between quick service pressure chamber  86  and brake cylinder pressure chamber  66  when post  92  has opened seat B against the bias of spring  90  and for closing of communication when post  92  is withdrawn by the movement of second valve stem  80  to allow check  88  to be biased into the closed position by spring  90 . 
         [0025]    When a brake application is made, brake pipe pressure initially flows from quick service pressure chamber  86  through open valve seat B to the underside of QSLV diaphragm  54  and brake cylinder pressure chamber  66  (and thus the brake cylinder). When the brake cylinder pressure in brake cylinder pressure chamber  66  reaches a threshold, e.g., nominally 10 psi, QSLV diaphragm  54  moves upward through distance C until valve seat B closes, thereby severing the communication between the brake pipe and the brake cylinder. As the brake cylinder pressure increases further, QSLV diaphragm  54  will continue to move axially upward against QSLV spring  72 , closing gap D until valve stem  58  moves into contact with valve cover  56 . Any further pressure increase in brake cylinder pressure chamber  66  will continue to move QSLV diaphragm  54  upward against the bias of spring  72  as valve stem  58  is held stationary by valve cover  56 , thereby opening seat A. When seat A is open, brake cylinder air can flow through the cylindrical clearance between stem  58  of valve  52  and a check valve bushing  94 . Check valve seat A closes when the sum of the BCM reference pressure in BCM reference pressure chamber  68  acting over the upper area of QSLV diaphragm  54  plus the force of QSLV spring  72  is equal to or greater than the brake cylinder pressure in brake cylinder pressure chamber  66  acting on the underside of diaphragm  54 . In this arrangement, the reference pressure is equal to the brake cylinder pressure minus the QSLV setting (e.g., nominally 10 psi) minus the amount of the check valve opening times the QSLV spring rate K. This results in a definable pressure offset equal to: 
         [0000]      Pressure Offset=[(height  D −height  C )* K ]/(wetted area of the diaphragm)
 
         [0026]    Referring to  FIG. 3 , another embodiment of a combined quick service check valve and brake cylinder maintaining valve  100  has many of the same components as valve  50 , but instead of check valve  52 , valve  100  includes a check valve seat A that is defined by a check valve  102  having a tapered cylindrical check valve stem  104  that passes through a check valve stem guide  106  in QSLV diaphragm  108  to define a cylindrical clearance therebetween. The cylindrical clearance is selectively opened and closed when check valve  102  is moved upwardly so that an O-ring is brought into sealing engagement with the cylindrical clearance. When check valve seat A is open, brake cylinder air flows from a brake cylinder pressure chamber  112  through the cylindrical clearance positioned between check valve stem  104  and check valve stem guide  106  and into a BCM reference pressure chamber  114  positioned on the top of QSLV diaphragm  108 . Check valve  102  closes when the reference pressure is sufficient to restore force balance as detailed above. A second seat B operates as discussed above with respect to system  50 . 
         [0027]    Referring to  FIG. 4 , a further embodiment of a combined quick service check valve and brake cylinder maintaining valve  120  comprises a check valve assembly  122  housed in a brake cylinder pressure chamber  124  of a bushing  126  and sealed against a resilient QSLV diaphragm  128  positioned in a valve cover  130  above brake cylinder pressure chamber  124  to define a first seat A. QSLV diaphragm  128  is biased downwardly by a QSLV spring  132  positioned in a spring guide  134  within valve cover  130 . Check valve  122  is held in sealing engagement with QSLV diaphragm  128  by a check valve spring  136  that is also positioned in brake cylinder pressure chamber  124  of bushing  126 . Check valve  122  is moveable upwardly through a distance D as QSLV diaphragm  128  until a shoulder  138  of check valve stem  122  engages a retaining ring  140  positioned in the bore of bushing  126 . When check valve stem  122  engages retaining ring  140  positioned in the bore of bushing  126 , valve stem  122  and diaphragm  128  separate, thereby opening seat A. A passage  142  formed through diaphragm  128  allows for communication between brake cylinder pressure chamber  124  positioned below diaphragm  128  and a BCM reference pressure chamber  144  positioned above diaphragm  128  when seat A is opened. Seat A is preferably formed by a profiled cylindrical seat surface  146  formed on the upper end of check valve  122  to securely seal against resilient QSLV diaphragm  128 . 
         [0028]    The opposing end of check valve  122  includes a post  148  extending through an internal passageway  150  and a bead seat  152  in the bore of bushing  126 . Post  148  further extends into a quick service pressure chamber  154  in a lower portion of the bore of bushing  126 . Post  148 , as in prior embodiments, provides for a clearance gap  156  with passageway  150  and extends into quick service pressure chamber  154  to engage a check  158  that is biased upwardly as in prior embodiments to define a second seat B. Check  158  can move upwardly a distance C before closing against bead seat  152 , and thus closing clearance gap  156  of passageway  150 . Seat B thus allows for communication between quick service pressure chamber  154  and brake cylinder pressure chamber  124  when post  148  has opened seat B, and closes communication between chambers  124  and  148  when post  148  is withdrawn and check  158  closes against bead seat  152 . 
         [0029]    As brake cylinder pressure increases in system  120 , QSLV diaphragm  128  is biased against QSLV spring  132  by air pressure in brake pressure chamber  124 . As QSLV diaphragm  128  is compressed upwardly, check valve  122  will move through distance D until shoulder  138  engages retaining ring  140 . Any additional brake cylinder pressure increases will further compress QSLV diaphragm  128  against QSLV spring  132 , thereby opening seat A as valve  122  can no longer move and will separate from diaphragm  128 , thereby opening passage  142  at seat A. When check valve seat A is open, brake cylinder air may flow from brake pressure chamber  124  through open seat A, and then through passage  142  formed in diaphragm  128 , to reach BCM reference pressure chamber  144  positioned above QSLV diaphragm  128 . Check valve  122  closes when the reference pressure is sufficient to restore force balance as detailed in the second embodiment above. Seat B operates as explained above with respect to prior embodiments. 
         [0030]    In yet another embodiment of the present invention, a combined quick service check valve and brake cylinder maintaining valve  160  comprises a check valve assembly  162  positioned in an upper portion  1  of a QSLV cap  166  and having a first seat A formed from a check  168  that is biased downwardly by a check valve spring  170  for selective engagement with a bead seat  172 . Bead seat  172  encloses an annular passage  174  formed through a shoulder  176  in QSLV cap  166 . Passage  174  permits communication between a brake cylinder pressure chamber  178  associated with upper portion  164  of cap  166  and a BCM reference pressure chamber associated with the lower portion  182  of cap  166 . Spring  170  is biased so that seat A is normally in a closed position. 
         [0031]    BCM reference pressure chamber  180  in lower portion  186  of cap  166  contains a QSLV spring  184  positioned in a spring guide  186  that engages a QSLV diaphragm  188  positioned in the lower side of BCM reference pressure chamber  180 . A stem  190  associated with diaphragm  188  extends upwardly through BCM reference pressure chamber  180  and into passageway  174  so that movement of diaphragm  188  upwardly against the bias of spring  184  will cause post  190  to move through a distance D to engage check  168  and open seat A. Distance D defines the amount of BCM pressure offset and is controlled by the length of check valve stem  190  and the distance to check valve  162 . 
         [0032]    A bushing  192  is positioned below diaphragm  188  and includes an upper portion defining a brake cylinder chamber  194  that is separated from a lower portion defining a quick service pressure chamber  196  by a narrow passageway  198 . A stem  200  having a lower post  202  is positioned in brake cylinder chamber  194  so that it engages diaphragm  188  at its upper end and post  202  extends through passageway  198  into quick service pressure chamber  196 . Quick service pressure chamber  196  includes a check  204  that is moveable through distance C to close of a second seat B, and thus passageway  198 , so that communication between brake cylinder pressure chamber  194  and quick service pressure chamber  196  is also closed as discussed in prior embodiments. 
         [0033]    As the brake cylinder pressure increases, QSLV spring  184  compresses until distance D is zero. Additional increase of brake cylinder pressure will further compresses QSLV diaphragm  188  and spring  184 , thereby opening check valve  162  at seat A. When check valve seat A is open, brake cylinder air flows through open seat A into BCM reference pressure chamber  180  on the top of QSLV diaphragm  188 . Check valve  162  closes when the reference pressure is sufficient to restore force balance, as explained in the other embodiments above.