Abstract:
An air bladder actuated railroad car retarder is designed to simplify installation, operate in a manner imposing minimal stress on the bladder, improve preventive maintenance, and simplify access to the main fulcrum bearings. The air bladder actuator is made with lightweight aluminum end plates and utilizes a unique stud assembly for attaching the actuator to the retarder pivot arms. Rigid mounting of the air bladder with a unique pivot geometry exposes the bladder to minimal lateral deflection which is balanced in both directions. A simple stroke limiter assembly, external to the air bladder, is also used to measure and monitor wear of the main fulcrum bearings. The stroke limiter assembly is easily demountable and removable to enhance access to the main fulcrum pivot for replacement of the fulcrum bearings.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a bladder-actuated low-profile railroad retarder that is particularly suited for a railroad marshalling yard. 
   Bladder actuators are well known in the railroad industry. In 1882, the Smith Vacuum Brake included a sack or collapsing cylinder. The Firestone AIRSTROKE actuator developed in the 1930s includes upper and lower plates and a flexible bladder secured around the perimeter of each plate to form an airtight interior. The actuator is inflated and deflated to control its height. Down and up stops are used to set the minimum and maximum height or stroke length (S L ) of the actuator. A bumper, a chain, a cable or metal stops can be located inside the actuator for this purpose. U.S. Reissue Pat. No. Re 33,207 discloses an on-board braking system using the Firestone actuator. U.S. Pat. No. 6,220,400 discloses a low profile, railway car retarder using the Firestone actuator. The actuator has an internal guide formed by two telescoping tubes, one of which has a stop ring at its end to form the upper and lower limit stops. 
   The railroad marshalling yard environment is dirty, rugged and non-stop. Retarders, switches, actuators, compressed air controls, related electric and electronic devices, and other components along tracks must withstand exposure to harsh weather, dirt, gravel, petroleum and other chemicals, and withstand being struck by moving objects carried by the cars. Moreover, actuators for retarders produce static vertical forces of about 20,000 pounds to generate the necessary braking power to control the speed of a fully loaded railroad car. Given this demanding environment, the railroad industry places great significance on minimizing maintenance and down time. Bladder actuators must withstand large cyclical loads and a harsh environment while maintaining low maintenance and down time requirements similar to conventional rigid cylinder actuators. The guide mechanism and limit stops of bladder actuators are often located inside the actuator for additional safety reasons. 
   A problem with railroad retarders is reducing maintenance to meet the demands of a busy marshalling yard setting. Evaluating fulcrum bearing wear is particularly problematic because the bearing is enclosed in the retarder. Conventional retarders must be disassembled to accurately and visually inspect of the bearing. Because closing a portion of the yard is impractical in a busy yard, maintenance personnel resort to using a pry bar to physically pry apart the upper and lower lever arms to determine if there is any wiggle occurring at the fulcrum bearing. Yet, this “wiggle” test is unreliable, particularly when done by a worker who is not familiar with the internal structure and mechanics of the retarder, and is not aware of the likely wear locations of the fulcrum bearing. If the pry bar is not inserted into the retarder and pushed or pulled in directions that will reveal the actual amount of wear, then the test may incorrectly indicate that little or no wear has occurred. Yet, a lack of proper inspection can result in an untimely failure of the fulcrum and retarder, which will then need to be replaced. Replacing a retarder is difficult to schedule because it requires a portion of the yard to be closed, which adversely impacts yard usage. Replacing a retarder during winter months when the ground is frozen is impractical. 
   Another concern with conventional retarders is the safety of yard maintenance personnel. The longer the workers are close to or in physical contact with the retarder, the more likely they are to be injured due to the daily risks associated with yard work. Inspecting bearing wear places workers at risk because the “wiggle” test requires a worker to stand on or near the retarder to manipulate the pry bar. The test is also inherently dangerous because of the awkward position and significant force a person must exert with the pry bar. Disassembling the retarder to inspect the bearing is even more involved, more time consuming, and more of a safety concern for the workers. 
   Another problem with conventional air bladder retarders is air consumption. The compressed air supply system for the yard has limited capacity. Conventional air bladder retarders use a significant amount of compressed air each time the retarder is activated. Installing numerous air bladder retarders throughout the yard can significantly increase yard air consumption. If the yard air system is already operating near capacity, installing air bladder retarders may require the addition of an air compressor or the replacement or overhauling of the of the air system. Yet, modifying or replacing the yard compressed air supply system is costly and time consuming, particularly regarding yard down time. 
   Another problem with air bladder retarders is life expectancy. Any crimping of the bladder during use can cause accelerated wear on the inside surface of the bladder. This wear weakens the bladder and can lead to premature rupturing. This problem is accentuated when the upper and lower plates of the bladder are pivotally connected to the lever arms by pivot pins. The pivot connections allow the plates to rotate, which can lead to undesired crimping. An additional guide mechanism is necessary to maintain the parallel alignment of the upper and lower plates of the bladder actuator. Bladder manufacturers set limits on the relative rotation of the plates when the bladder is in its fully extended or fully collapsed positions. Crimping can occur when the bladder is allowed to arc or accordion out due to relative rotation of the plates. 
   Another problem with conventional air bladder retarders is predictable use and service requirements. A problem with using an air bladder as an actuator for a railroad retarder is that it is difficult to identify or measure the wear on the bladder such as internal wear caused by crimping. Disassembling the actuator to inspect the bladder involves safety risks, maintenance costs and yard down time. Still, even a small leak in the bladder will waist yard air. Any unpredicted, premature rupture of the bladder will disable the retarder, lead to unplanned and costly replacement and down time, and increase safety risks to yard maintenance personnel. 
   Another problem with bladder actuators is the design of the guide mechanism. Some bladder actuators use an internal guide rod to form the upper and lower limit stops of the actuator as in U.S. Pat. No. 6,220,400. The guide rod experiences a tension load in excess of 20,000 pounds each time the actuator is opened. This cyclical load loosens the threaded engagement of the guide rod to the upper plate. Yet, maintaining the alignment of the guide rod is critical. Even a slight loosening of the guide rod can result in some lateral movement, which will exponentially increase the loads on and wear rate of the internal bushing or bearing. This loosening of the guide rod, or even the potential loosening of the guide rod, significantly increases the need for routine maintenance and possible down time. Other bladder actuators rely on the fulcrum pin to guide the movement of the actuator plates. Yet, the upper and lower plates for these bladder actuators also join the upper and lower lever arms via pivot pins. This construction can lead to crimping of the bladder, and result in leaks and unpredicted rupture of the bladder. 
   The present invention is directed to solving these and other problems. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a bladder actuated retarder for a rail car includes a stroke limiter linkage assembly, the change in position of which can be monitored to provide an accurate indication of fulcrum bearing wear. The invention is applied to a conventional retarder apparatus including an upper lever arm that is pivotally connected to a lower lever arm with a fulcrum pin assembly. The fulcrum pin assembly includes a pin carried in a cylindrical bearing and rotatable therein. The lever arms have opposed ends to each of which is connected an end of an extensible bladder actuator that is operative to cause relative rotation of the lever arms on the fulcrum pin and to move the opposed ends of the arms apart. In accordance with the present invention, the actuator stroke limiter linkage assembly interconnects the lever arms at a location between the arms and between the fulcrum pin and the actuator to prevent extension of the actuator beyond a desired limit. The stroke limiter assembly is also operative to limit compression of the bladder actuator beyond the limit of collapse recommended by the manufacturer. 
   In accordance with a preferred embodiment of the invention, the stroke limiter assembly includes a stop link having one end pivotally connected to one of the lever arms and a slotted opposite end receiving a pivot pin for connection to the other lever arm. The slotted end has a stop surface that is engageable by the pivot pin at the desired limit of actuator extension and an opposite stop surface that is engageable by the pivot pin at the desired limit of actuator retraction. The rotational position of the stop link with respect to the other lever arm, when the stop surface is in engagement with the pivot pin, varies with wear of the cylindrical bearing. Means are provided for measuring the rotational position of the stop link to monitor bearing wear. Preferably, the measuring means comprises a reference surface on the other lever arm and a reference face on the stop link. The reference surface and reference face are positioned transverse to the arc of stop link rotation such that a change in the angle between the reference face and the reference surface provides a quantitative indicia of bearing wear. 
   In a preferred embodiment, the stroke limiter assembly is detachable from its operative position to provide access to the fulcrum pin assembly. 
   The bladder actuator preferably comprises a rubber air bladder that is operable between a pressurized extended position and a collapsed retracted position. The air bladder includes an expandable rubber bladder member, a pair of aluminum end plates enclosing opposite ends of the bladder with air-tight seals. A series of machine screws are threaded into tapped holes in the end plates, the screws oriented with their screw heads on the interior of the end plates and with flexible sealing rings compressed therebetween. Mounting brackets are rigidly attached to the opposed ends of the lever arms and each mounting bracket has a series of through bores for receipt of the threaded ends of the machine screws. A series of nuts connect the screws to the mounting brackets. 
   In a further embodiment of the invention, the space within the bladder when the bladder is in the collapsed retracted position is provided with a spacer material that substantially fills the collapsed internal volume. The spacer material is preferably made from a lightweight plastic foam. 
   The retarder apparatus of the present invention preferably includes a lever arm counterbalance means for causing the opposed ends of the lever arms, connected to opposite ends of the air bladder, to move toward one another when the air bladder is moved to its collapsed position. 
   In a further embodiment of the invention, the air bladder actuator comprises an expandable rubber bladder member, a pair of rigid end plates that enclose opposite ends of the bladder member with air-tight seals, and mounting brackets that provide rigid connections between the end plates and the opposed ends of the lever arms. The end plates are oriented, in use, to diverge in a direction away from the fulcrum pin in the extended position of the bladder and to move through a neutral position to a position in which the end plates converge in the direction away from the fulcrum pin, whereby lateral deflection of the bladder member is balanced and minimized. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation view, partly in section, showing an air bladder-operated rail car retarder in operative association with a rail and a car wheel. 
       FIG. 2  is a vertical section taken on line  2 - 2  of  FIG. 1 . 
       FIG. 3A  is a side elevation view similar to  FIG. 1  showing the air bladder in its fully extended position. 
       FIG. 3B  is a side elevation view similar to  FIG. 3   a  showing the air bladder in a mid-stroke position. 
       FIG. 3C  is a side elevation similar to  FIGS. 3A and 3B  showing the air bladder in a retracted fully collapsed position. 
       FIG. 4  is a vertical section taken on line  4 - 4  of  FIG. 1 . 
       FIG. 5  is a side elevation of the retarder shown in  FIG. 1 , with parts removed for clarity, showing the means for monitoring fulcrum bearing wear in accordance with the present invention. 
       FIG. 6  is a side elevation, partly in section, of the preferred construction of the air bladder used in the retarder of the subject invention. 
       FIG. 7  is an upper perspective view of the air bladder retarder of the present invention in its installed operative position in association with a rail, car wheel and rail ties. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring initially to  FIGS. 1 and 7 , a pneumatic retarder  10  of the present invention is used to control the speed of a moving car in a marshalling yard by engaging opposite faces of a car wheel  11  as it rolls on a rail  12  through the retarder. The retarder  10  is positioned between adjacent ties and extends beneath the rail  12  from an outer field side of the rail to an inner cage side between the rails  12  (only one of which is shown in the drawings). A support structure  19  for the retarder includes substantially identical supports  29  carried by the ties and positioned in opposite sides of the retarder. 
   The retarder  10  has an upper lever arm  14  and a lower lever arm  15  which are pivotally connected with a fulcrum pin assembly  16  positioned directly beneath the rail  12 . On the field side of the retarder, the lever arms  14  and  15  have opposed ends to each of which is attached an end of an air bladder actuator  17 . The fulcrum end of the upper lever arm  14  has a bifurcated construction defined by a pair of legs  18  provided with aligned through bores  20 . The lower lever arm  15 , near the end remote from the air bladder actuator  17 , is provided with a cylindrical boss  21  having a through bore  22  of the same diameter as the through bores  20  in the legs of the upper lever arm  14 . Each of the through bores  20  is provided with a sleeve bearing  23  and, similarly, the through bore  22  is provided with two sleeve bearings  24  identical to the sleeve bearings  23 . In assembly, the cylindrical boss  21  of the lower lever arm  15  is received between the legs  18  of the upper lever arm and pivotally connected thereto with a fulcrum pin  25 . 
   As shown in  FIG. 1 , the upper lever arm  14 , adjacent the fulcrum pin assembly  16 , is provided with a horizontal mounting surface  26  for a brake beam assembly  27 . Similarly, the lower lever arm  15  is provided with a horizontal mounting surface  28  for mounting a brake beam assembly  30 . Each of the brake beam assemblies  27  and  30  is essentially the same and includes a brake beam  31  to one end of which is attached an L-shaped brake pad or bar  33 . Each brake beam assembly  27  and  30  also includes a thrust block  32  positioned against the opposite end of the brake beam  31 . Shims  34  for adjusting and setting the desired braking position of the brake pads  33  are placed between the thrust block and a stop block  35  formed as a part of the upper lever arm  14 . The thrust block and shims are secured to the stop block  35  with bolted connections. Similarly, the brake beam assembly  30  for the lower lever arm  15  is attached to the mounting surface  28  with bolted connections through stop block  36 . 
   When the air bladder actuator  17  is pressurized, it expands and extends to force the attached ends of the upper and lower lever arms  14  and  15  apart which motion is translated through the fulcrum pin assembly  16  to cause the brake pads  33  to move toward one another and engage opposite faces of the car wheel  11  with a desired braking force, as shown in  FIG. 3A . When it is desired to remove the braking force, the pressure in the air bladder is released and the ends of the lever arms  14  and  15  move relatively toward one another, through the mid-stroke position shown in  FIG. 3B  to the final retracted and collapsed position shown in  FIG. 3C . In moving to the  FIG. 3C  position, the upper lever arm  14  moves under the force of gravity downwardly until a pair of cushioned stops  37  engage a fixed frame member  38  on the support  29 . This movement, of course, also causes the upper lever arm brake pads  33  to move away from the rail and car wheel  11 . Similarly, the force of gravity would also tend to move the lower lever arm  15  downwardly. However, because the lower lever arm brake pad  33  must also be moved away from the rail and car wheel  11 , a compression spring  40  on the end of the lower lever arm  15 , and in operative engagement with the support  29 , forces the actuator end of the lower lever arm upwardly and the brake pad  33  to move away from its braking position. The compression spring arrangement  40  is carefully designed and adjusted to move the lower lever arm upwardly, as indicated, but not to also lift the upper lever arm  14  off the stops  37 . 
   Referring also to  FIG. 6 , the air bladder actuator  17  includes a conventional rubber air bladder  41  of a type identified above. However, instead of utilizing conventional steel end plates, the preferred embodiment of the air bladder actuator  17  of the present invention utilizes aluminum end plates  42 . The substitution of aluminum end plates reduces considerably the weight of the actuator  17  such that it is within the limit safely lifted by one person. Its weight of less than 50 lbs. (about 23 kg) is within the lifting limits adhered to in the rail industry. However, care must be taken to avoid stripping threaded connections in aluminum which are much softer and more easily damaged than are steel. To connect the end plates  42  to the respective upper and lower lever arms  14  and  15 , each end plate  42  is tapped for four machine screws  43 . A sealing ring  44  is placed on the screw shank and the bolt is threaded from the inside through the tapped hole in the end plate to compress the sealing ring  44  between the screw head and the inside face of the plate  42 . Preferably, suitable thread locking compound is applied to the screw threads as well. Sealing ring  44  is preferably a Stat-O-Seal ring made by Parker Hannifin Corporation. The net effect of mounting the machine screws  43  as indicated is to enable them to act like threaded studs and without concern for the damaging the tapped holes in the aluminum end plates  42 . Furthermore, an extremely effective air seal is created for the air bladder  41 . 
   Attachment of the upper and lower aluminum end plates  42  to the respective upper and lower lever arms  14  and  15  is accomplished by the use of upper and lower mounting brackets  45  and  46 , respectively. Referring also to  FIG. 7 , the upper mounting bracket  45  is generally U-shaped and includes a pair of legs  47  connected by a web  48 . Each of the legs  47  is connected to an end arm  50  of the upper lever arm with two plug welds  51 . The web  48  is connected directly to the machine screws  43  secured in the end plate  42  with suitable nuts  52  and washers. The lower mounting bracket  46  is also U-shaped and has a pair of legs  53  interconnected by a web  54 . The legs are attached to an end arm  55  of the lower lever arm  15  with connecting bolts  56 . Each of the connections between the upper lever arm end arms  50  and the legs  47  of the mounting bracket are made with two plug welds  51 . Two connecting bolts  56  are used to connect each lower mounting bracket leg  53  to the lower lever end arm  55 . The connection of the air bladder actuator  17  to the upper and lower lever arms  14  and  15  is thus rigid and immovable. 
   As mentioned in the Background above, manufacturers of air bladders of the type used in the present invention caution against excessive lateral deflection of the bladder in use which may result in crimping and premature failure. One prior art solution to this problem is to utilize a guide rod or other linear guiding mechanism on the interior of the bladder. The bladder actuator end plates are then pivotally connected to the upper and lower lever arms, rather than with the rigid connections used in the apparatus of the present invention. Internal guide mechanisms are heavy and expensive, but are, nevertheless, subject to high loads and the risk of failure. 
   The connections of the air bladder end plates  42  to the upper and lower lever arms  14  and  15  in the construction of the present invention holds the rubber air bladder  41  securely against excessive lateral deflection and, moreover, minimizes lateral deflection in either direction as compared to prior art devices. Referring again to  FIGS. 3A-3C , lateral deflection of the air bladder  41  (in the direction of the length of the lever arms  14  and  15 ) is minimized and balanced as the bladder flexes from the fully extended  FIG. 3A  position to the fully collapsed  FIG. 3C  position. More particularly, the actuator end plates  42  are positioned to diverge in the direction away from the fulcrum pin  25  in the extended  FIG. 3A  position. As the bladder collapses to the neutral mid-stroke position of  FIG. 3B , the end plates  42  assume a parallel orientation. As the bladder compresses further to its fully collapsed  FIG. 3C  position, the mounting plates assume a convergent position in the direction away from the fulcrum pin. In this manner, the air bladder flexes laterally in both directions, each of which is a minimal deflection, well within the limits recommended by the manufacturer, and far short of resulting in potentially damaging crimping. 
   Referring also to  FIGS. 4 and 5 , the retarder  10  must be provided with an actuator stroke limiter to prevent the air bladder  41  from being extended beyond the limits set by the manufacturer and by the requirements of the maximum braking force desired to be applied to the car wheels  11 . Because the use of guide and stop means that are internal to the air bladder actuator are fraught with high cost, complexity and unreliability, the retarder of the present invention utilizes a simple stroke limiter linkage assembly  57  that operates effectively and reliably, can be easily removed if necessary to access the fulcrum pin assembly  16 , and can also be used to monitor wear of the fulcrum bearings as will be described in detail below. The stroke limiter assembly  57  includes a pair of parallel stop links  58  that are pivotally attached to the lower lever arm  14  with a lower pivot pin  60 . The upper opposite ends of the stop links  58  are provided with slots  61  dimensioned to receive an upper pivot pin  62  extending through the slots  61  and pivotally mounted in a pair of mounting ears  63  extending downwardly from the underside of the upper lever arm  14 . The stop links  58  are maintained in a parallel spaced orientation by a spacer bushing  64 . When the air bladder actuator  17  is pressurized and caused to expand, the upper pivot pin  62  moves upwardly in the slots  61  until it engages stop surfaces  65  defined by the upper edges of the slots  61 , as shown in  FIGS. 1 and 5 . To limit the maximum retracted or collapsed position of the air bladder, the opposite ends of the slots  61  in the stop links  58  provide down stop surfaces  69  which are engaged by the upper pivot pin  62  to halt compression of the bladder at a limit prescribed by the manufacturer. The outer ends of each of the pins  60  and  62  may be secured against axial displacement with simple cotter pin connections  59 . When it is desired to disassemble or remove the stroke limiter assembly, as for access to the fulcrum pin or to repair or replace the stroke limiter assembly itself, the removal of two cotter pins  59  is all that is required. 
   Referring particularly to  FIG. 5 , the rugged operating conditions and high operating loads to which the retarder  10  is exposed in service result in wear of the fulcrum sleeve bearings  23  and  24 . Such wear inherently leads to looseness in the fulcrum pin assembly, the extent of which has been difficult to determine in prior art retarders, as mentioned in the Background description above. The cylindrical sleeve bearings  23  and  24  typically have a wall thickness of 0.375 inch (about 10 mm). As the upper lever arm bearings  23  wear, the upper lever arm will move laterally away from the fulcrum pivot (to the left in  FIG. 5 ) by a maximum amount of 0.375 inch. Similarly, wear of the lower lever arm bearings  24  will result in movement of the lower lever arm as much as 0.375 inch in the opposite direction. 
   This could result in a total displacement of the lever arms with respect to one another of 0.750 inch (about 20 mm). This displacement of the lever arms is reflected directly in increased pivotal movement within the stroke limiter assembly  57 . Specifically, as bearing wear increases, the position of the stop links  58  with respect to the mounting ears  63  and upper lever arm  14  changes in a generally linear relation. When the bearings are new and there is no “wiggle” in the fulcrum pin assembly  16 , the angle between a machined reference surface  66  on the underside of the upper lever arm  14  and a reference face  67  on one of the stop links  58  can be measured when the bladder is fully extended, as with a digital protractor. In the example shown in  FIG. 5 , the angle in a new bearing, no-wiggle situation is 97°. At full wear displacement of 0.750 inch, the angle increases to 104°. This provides the ability to monitor bearing wear in a simple, safe and cost-effective manner and to take the retarder out of service for bearing replacement in a scheduled manner that avoids unexpected failure. When bearing replacement becomes necessary, the stroke limiter assembly  57  can be easily taken apart to permit access to the fulcrum pin assembly  16 , including the bearings  23  and  24 . 
   The subject invention also addresses the problem associated with the high volume of compressed air required to operate a air bladder actuator. First of all, in its inactive retracted and collapsed position, the air bladder still defines a considerable open internal volume. Upon actuation to extend the bladder, the collapsed internal volume must first be pressurized and then additional compressed air must be utilized to extend the bladder. In one embodiment of the present invention, an internal spacer  39  as shown in  FIG. 6 , is placed inside the bladder actuator  17  before the second aluminum end plate  42  is attached. The spacer preferably is a solid piece of lightweight material of cylindrical shape that will substantially fill, but have a volume somewhat less than the collapsed internal volume of the actuator. The spacer is preferably made from a lightweight plastic foam, such as closed-cell polyurethane. 
   Referring again to  FIG. 1 , a load bearing land  68  is welded to the outside of each of the legs  47  and extends under one of the end arms  50  of the upper lever arm  14 . Land  68  provides two functions. First of all, in assembly, the surface of the land is brought into contact with the reference surface  66  to accurately locate the bracket with respect to the end arm  50  for making the plug welds  51 . In addition, land  68  provides a direct load bearing path between the upper lever arm and the bladder mounting bracket  45  so that the plug welds  51  do not have to transmit operating load. In the remote event of plug weld failure, the load bearing land  68  would also continue to function to bear full operating load. 
   A similar arrangement is provided for the lower lever arm  15  and the lower mounting bracket  46 . A lower load bearing land  70  is welded or otherwise secured between the opposite inside faces of the legs  53  of the lower mounting bracket  46 . The land  70  is positioned to accurately locate the bracket with respect to the end arm  55  of the lower lever arm  15  to facilitate making the connection via connecting bolts  56 . In addition, as with the upper load bearing land  68 , the lower land  70  provides a direct load bearing path between the lower mounting bracket  46  and the lever arm  15  such that the connecting bolts  56  do not have to carry the operating load. In some prior art devices, similar connecting bolts that are responsible for full transmission of the operating load have been known to loosen in service, resulting in poor performance and potential failure.