Patent Publication Number: US-8123309-B2

Title: Dual seal brake control valve

Description:
BACKGROUND AND SUMMARY OF THE DISCLOSURE 
     The present disclosure relates generally to brake control valve systems for operating a vehicle&#39;s air brakes, in response to brake pipe pressure in a brake pipe, and more specifically to a brake control valve system which is insensitive to increased mechanical vibrations and brake pipe pressure fluctuations or noise. 
     Brake control valve systems for a vehicle having air brakes generally include a brake control valve responsive to the brake pipe pressure in a brake pipe to operate the brakes of a vehicle. For a reduction of brake pipe pressure, the brakes are proportionally applied. For an increase in brake pipe pressure, the brakes may be released totally or gradually. In the American Association of Railroads AAR system, the brake control valves include a service section and an emergency section which are responsive respectfully to a service rate of reduction and emergency rate of reduction to apply the brakes appropriately. Each section includes a separate diaphragm or piston responsive to the brake pipe pressure on one side and a reference pressure on the other. Not only must the brake control valve differentiate between a service and an emergency application, but also must react in a specific amount of time to apply the brakes and propagate the signal throughout the brake system. 
     Historically, the control valves have been designed to be substantially insensitive to pneumatic noise signals in the brake pipe which could cause undesired emergency (UDE) braking and undesired release (UDR). Various mechanisms have been used, for example, chokes or restrictions interconnecting the brake pipe and the reference chamber of the diaphragms, to accommodate pneumatic noise. One of the sources of the pneumatic noise or shock is the mechanical vibration of the vehicle. A major identifiable source of this mechanical vibration is in the longitudinal motion or slack action between the different cars of the vehicle or train. The insensitivity or the stability built into the brake control valves to accommodate the pneumatic noise or shock have, unbeknownst to the designers, accommodated and therefore masked, mechanically produced vibration on the brake control valve which can produce undesired minimum (UDM) service braking. 
     With the introduction of aluminum and other building materials as well as the modification of other portions of a car of a train, the empty car gross weight has been reduced from the range of 55,000 to 65,000 lbs. to 40,000 to 45,000 lbs. For these lighter cars, it has been noticed that the control brake valves had been experiencing an undesired minimum service application. 
     Experimentation has shown that the undesired minimum service application is a function of the horizontal G-forces and its duration. For a low horizontal G-force in the range of 5 to 7 Gs, typical duration of 2.6 to 2.7 milliseconds generally does not produce an undesired minimum service application. For larger residual durations, larger vertical G-forces result during the residual 4.6 milliseconds of 5.2 milliseconds producing undesirable minimum service brake application. Vertical acceleration produced by horizontal impact in the range of approximately plus and minus ±15 Gs has been observed. 
     This increased vertical force, that the differential motion between the service piston and the housing will cause the service piston to operate the quick service chamber check valve in the downward motion of the oscillating valve. This opening, even though for short periods of time, has been sufficient to trigger a minimum service application. Thus in addition to the previously recognized horizontal buff and draft forces, the control valve is also subjected to significant vibration and vertical shock components during slack action. 
     The present design provides a service valve which less sensitive to mechanically produced vibrations. The brake control valve includes a housing, a quick braking chamber and a piston subject to brake pipe pressure on one side of the piston. A bore in the housing connects the quick braking chamber at a first end and the one side of the piston at a second end. A first valve is in the housing at the first end of the bore. A first operator is in the bore for opening the first valve for a range of positions of the piston. The bore has a first portion of a first diameter and a second portion of a second diameter larger than the first diameter. The first bore portion connects the one side of the piston to the second bore portion. A first operator in the bore is connected to the piston. A seal on the first operator is dimensioned to form a seal with the first bore portion and not with the second bore portion. The seal is located on the operator to lie in the first bore portion for a first segment of the range of piston positions and to lie in the second bore portion for a second segment of the range of piston positions. 
     A second valve in the housing connects a brake cylinder port with a reservoir port when opened. A second operator in the housing is connected to the first operator for opening the second valve in the second segment of the range of piston positions. 
     The bore includes a third bore portion connecting the second bore portion to the first valve and of a third diameter and a second port is connected to the quick braking chamber. The first operator has a tip portion of a fourth diameter substantially equal to the third diameter and has an adjacent portion of a fifth diameter smaller than the fourth diameter. The tip portion has a length less than the first segment of the range. 
     The bore may include a tapered bore portion between the first and second bore portions and the seal lies in the tapered bore portion for a portion of the second segment of the range of piston positions. 
     A kit includes a bushing and a first operator which is to be connected to a piston of the brake control valve and is to extend from the piston through a bore of the bushing from a first end of the bore to a valve seat at a second end of the busing. The bore has a first bore portion of a first diameter adjacent the first end of bore and a second portion of a second diameter larger than the first diameter adjacent the second end of bore. A seal on the first operator is dimensioned to form a seal with the first bore portion and not with the second bore portion. The seal is located on the operator to lie in the first bore portion for a first segment of a range of piston positions and to lie in the second bore portion for a second segment of the range of piston positions. 
     The bore may include a third bore portion connecting the second bore portion to the valve seat and of a third diameter and a second port is connected and axial to the bore. The first operator has a tip portion of a fourth diameter substantially equal to the third diameter and has an adjacent portion of a fifth diameter smaller than the fourth diameter. The tip portion has a length less than the first segment of the range. 
     The bore may include a tapered bore portion between the first and second bore portions and the seal lies in the tapered bore portion for a portion of the second segment of the range of piston positions. 
     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a portion of a service portion of a brake control valve in the charging lap position according to the prior art. 
         FIG. 2  is a cross-sectional view of a kit including a bushing, first and second operators and a piston stem according to the present design 
         FIG. 3  is a schematic view of  FIG. 1  with the kit of  FIG. 2  in the first stage of quick service. 
         FIG. 4  is a schematic view in a second stage of quick service. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The present design is being described with respect to an improvement on a DB-60 control valve available from New York Air Brake Corporation, a unit of Knorr Brake Holding Corporation, of Watertown, N.Y. A detailed description of the complete DB-60 control valve is found in instruction manual MU-21 available from New York Air Brake. Although the improvement has been incorporated into the service section of the DB-60, the present improvement may be provided to any brake control valve portion which includes a piston responsive to brake pipe pressure on one side thereof. Thus, the present design may be used in other AAR styled brake control valves or non-AAR brake control valves. Only those portions of the service section of the DB-60 which explain the operation of the present invention have been included in the schematics and others have been intentionally deleted for sake of clarity. 
     The brake control valve includes a housing  10  having a service piston  12  with brake pipe pressure in the top chamber  14  connected to the brake pipe BP by passage  16 . The bottom chamber  18  on the other side of the piston  12  is connected to the auxiliary reservoir AR through passage  20 . An auxiliary reservoir charging valve  22  is controlled by the piston  12  through operator  24  and includes spring  21 . The auxiliary reservoir charging valve  22  is connected to the brake pipe BP by sensitivity choke  26  in passage  28 . A stability choke  30  connects the brake pipe chamber  14  on the top of diaphragm  12  to the auxiliary reservoir AR by passage  32 . Whereas the sensitivity choke  26  interconnects the two chambers  14  and  18  of the piston  12  as long as the auxiliary reservoir charging valve  22  is open, the stability choke  30  interconnects the two chambers  14 ,  18  for all service positions of the service piston  12  and is closed off in the emergency position of the service position  12 . The restrictions  26  and  30  define the sensitivity of the service position  12  against pneumatic noises in the brake pipe. 
     A quick service inlet valve  40  includes a seat  42  and connects the top or brake pipe chamber  14  of piston  12  to the quick service chamber or volume  44 . Operator  46 , extending from the service piston  12 , includes a guide portion  48  moving within bore  50  of the housing. A passage  52  in the guide  48  connects the brake pipe chamber  14  of the piston  12  to the bore  50 . A smaller bore  58  connects bore  50  to the valve seat  42 . The operator  46  includes a first portion  54  of a first cross-sectional area or diameter and a second contiguous portion  56  of a second cross-sectional area or diameter smaller than the first cross-sectional area  54 . The first portion  54  engages the quick service inlet valve  40 . Portions  54  and  56  define restrictions between themselves and the bore  58 . The restriction formed by portion  54  is sufficiently small so as to minimize the flow to the quick service chamber  44 , whereas the restriction formed between bore  58  and portion  56  permits a flow rate to provide normal operation of the quick service inlet valve  40 . 
     The cross-section of the portion  54  and  56  of the actuator has been exaggerated in the drawings to illustrate the present invention. For example, the bore  58  would have a diameter of approximately 5.02 millimeters, the fast portion  54  would have a diameter of 4.92 millimeters and the portion  56  would have a diameter of 4.69 millimeters. The effective length of the first section  54  would be approximately 1.5 millimeters (2.0 millimeters less 0.5 millimeters of the valve seat  42 ). Thus, for the first 1.5 millimeters of travel of the piston  12  during the opening of the quick service inlet valve  40 , the flow through the open valve  40  is defined by the restriction between the first portion  54  and the bore  58 . For the remainder of the travel of the piston  12 , the flow is defined by the restriction between the second portion  56  and the bore  58 . 
     This design provides 75 percent less annular area during the initial 1.5 millimeters of travel and 140 percent more annular area during subsequent travel than the standard design. The restriction between portion  54  and bore  58  is selected to be insufficient to reduce the brake pipe pressure in chamber  14  to cause the piston  12  to become unstable and assume a braking position. 
     A spring cage  60  connects a spring  62  to the quick service inlet valve  40  and biases it closed. A slide or second operator  64  is operatively connected to the quick service inlet valve  40 , and includes a passage  66 , which in  FIG. 1  connects exhaust EXH through passage  68  in the housing to the brake cylinder by passage  70  in the housing. O ring  72  and K ring  74  on the slide  64  seals the slide in the bore  73  of the housing. A brake cylinder inlet valve  76  including spring  78  connects the brake cylinder passage BC  70  to the auxiliary reservoir via passage  80 . The slide  64  operates the brake cylinder valve  76  in response  35  to the quick service inlet valve  40 . 
     A balancing valve  82  with spring  84  includes an operator  86  which is controlled by the service piston  12 . A passage  88  in the operator  86  connects the auxiliary reservoir chamber  18  at the bottom of service piston  12  to a balancing piston  92  via passage  90 , when the balancing valve  82  is closed and passage  88  is opened. The balancing piston  92  has chamber  94  on its top side connected to exhaust EXH. A spring  96  resting on spring cage  98  biases the service system  12  towards its braking position. The spring cage  98  rests on shoulder  100  of an element  102  connected to the service piston  12 . An extension  104  of the balancing piston  102  will engage the spring cage  98  to change the biasing of the spring  96 . 
     The details of the operation of the brake valve illustrated in  FIG. 1  are described in U.S. Pat. No. 5,387,030. 
     As illustrated in  FIG. 2 , a shoulder  41  of operator or piston stem  46  receives the plates of the diaphragm  12  which are secured thereto by a nut, not shown, which is received on the threaded portion  43  of piston stem  46 . The guide  48  rides in the bore portion  50 . The guide  48  may or may not include the passages  52 . 
     The piston stem  46  receives the first operator or actuator having the portions  54  and  56 . In the illustrated operator, the diameter of the portions  54  and  56  are the same and correspond to the diameters of  FIG. 1 . The first operator includes an enlarged diameter portion  120  with a seal  122  on the circumference thereof. Although the seal  122  is shown as an O-ring, it may also be a K-ring. The portion  120  has a larger diameter than the portions  54  and  56 . 
     A bushing  110  includes the bore portions  50  and  58  connected by bore portions  112  and  114 . The bore portion  114  is a tapered transition between the larger bore portion  112  and the bore portion  50 . The operator portion  120  and seal  122  are dimensioned to form a seal with the bore portion  50  and not with the bore portions  112  and  114 . The operator portion  120  and seal  122  located on the operator to lie in the bore portion  50  for a first segment of the range of piston positions and to lie in the bore portions  112  and  114  for a second segment of the range of piston positions. 
     In addition to the port at the end of bore portion  58 , the bushing includes ports  116  connected to the quick service chamber  44 . The quick service inlet valve  40  is received on valve seat  42  on the bushing  110 . The top chamber  14  of the piston  12  is connected to the quick service chamber  44  only when the operator portion  120  does not form a seal with the bore portion  50 . This is illustrated in  FIGS. 3 and 4 . The connection is mainly through ports  116  with a secondary connection through bore portion  58 . If the operator includes the portions  54  and  56  of  FIG. 1 , the secondary connection flow is increased. 
     For small or first segment of the range of upward movement of the piston  12  and the operator  56 , the operator portion  120  moves in and maintains a seal with the bore portion  50 . The end  54  of the operator  56  moves the valve  40  off the valve seat  42  and the slide or second operator  56  in the first segment. Thus even though the valve  40  is lifted off the valve seat  42 , there is no air flow through the valve seat  40 . The operator  64  not in contact with the brake cylinder inlet valve  76  and the passage  66  connects the brake cylinder passage  70  with the exhaust passage  68 . 
     At the beginning of a second segment of the range of upward movement of the piston  12  and the operator  56 , the operator portion  120  moves in the tapered bore portion  112  and breaks the seal. This is shown in  FIG. 3 . Air from the top chamber  14  of the piston  12  slowly flows at a first rate mainly through bore portion  58  because of the taper. This begins the acceleration of the pressure drop in the top chamber  14  and results in further upward movement of the piston  12  and the operator  56 . 
     The operator  64  comes in contact with the brake cylinder inlet valve  76  and seals the passage  66 . This is the lap position cutting the brake cylinder passage  70  from exhaust passage  68  and the auxiliary reservoir passage  80 . 
     With further upward movement in the second segment of the range of upward movement of the piston  12  and the operator  56 , the operator portion  120  moves in the large bore portion  114  and with unrestricted flow around the operator portion  120 . This is shown in  FIG. 4 . Air from the top chamber  14  of the piston  12  freely flows at a second higher rate through the bore portion  58 . This further increases acceleration of the pressure drop in the top chamber  14  and results in quicker upward movement of the piston  12  and the operator  56 . This further upward movement of the piston  12 , operator  56  and operator  64  opens the brake cylinder inlet valve  76  connects the brake cylinder passage  70  and the auxiliary reservoir passage  80 . 
     The bushing  110  and the first operator  56  may be provided as a kit used to upgrade existing brake control valves. No modification of the housing  10  in the other portions of the brake control valve is required. 
     The present design decreases the sensitivity of the brake control valve to vibration induced motion of the piston. Although the present disclosure has been described and illustrated in detail, it is to be clearly understood that this is done by way of illustration and example only and is not to be taken by way of limitation. The scope of the present disclosure is to be limited only by the terms of the appended claims.