Abstract:
An air bladder actuator for a railroad car retarder utilizes a simplified stroke limiting arrangement that can be used in new actuator construction or applied as a retrofit assembly to an existing air cylinder actuated retarder.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application relates to and claims priority from U.S. Provisional Application Ser. No. 61/167,625, filed on Apr. 8, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention pertains to an air bladder actuated railroad car retarder and, more particularly, to a simplified and low cost internal stroke limiting arrangement for an air bladder cylinder used in the retarder. 
     Air bladder actuators are well known in the railroad industry and are now commonly used to operate retarders in railroad marshalling yards. One commonly used air bladder is a Firestone AIRSTROKE actuator. The actuator includes a flexible bladder that is secured around the perimeter on opposite ends to a pair of end plates to form an air tight interior. The bladder is inflated and deflated to control its length and stops are used to set the maximum and minimum stroke lengths of the actuator. The stroke limiting arrangement is preferably provided on the interior of the bladder between the end plates. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a stroke limiting arrangement is provided on the interior of the bladder that is rugged, yet of low cost. The bladder actuator is capable of use in retrofit applications to replace air cylinders in existing retarders. The retrofit arrangement reuses components of the air cylinder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation view in partial section, of a prior art air cylinder actuated retarder which can be retrofitted with a conventional air bladder actuator utilizing the internal stroke control apparatus of the present invention. 
         FIG. 2  is a side elevation view of a prior art air bladder actuated retarder utilizing a conventional double convolution air bladder actuator of the type identified above. 
         FIG. 3  is a side elevation view of a retrofit air bladder cylinder in accordance with the present invention. 
         FIG. 4  is an enlarged detail, partly in section, showing a retrofit air bladder retarder in accordance with the present invention. 
         FIG. 5  is an exploded view of a retrofit stroke limiter assembly for use in the retarder shown in  FIG. 1 . 
         FIG. 6  is a sectional view of a retrofit air bladder actuator of the present invention taken on line  6 - 6  of  FIG. 4  showing the retracted position of the actuator. 
         FIG. 7  is an enlarged sectional view taken on line  6 - 6  of  FIG. 4  showing the retrofit air bladder actuator in its extended position. 
         FIG. 8  is a sectional view similar to  FIG. 6  showing an air bladder actuator of the present invention newly manufactured without retrofit parts. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In retrofitting an air cylinder actuated retarder  10  of the prior art type shown in  FIG. 1 , the air cylinder  12  is removed, but several components are retained, machined as may be necessary, and incorporated into an internal stroke limiting mechanism for an air bladder  13  ( FIG. 3 ) that replaces the air cylinder  12 . The air cylinder upper end plate  14  is cut from the cylinder body  15 . The upper end plate  14  includes an integral pivotal clevis mount  16  which is also retained for use in the retrofit apparatus. The piston rod  17  of the air cylinder is also retained for reuse, but the piston head  18  is removed and not reused. 
     Referring also to  FIGS. 4 and 5 , the peripheral edge of the upper end plate  14  is provided with a circular bolt hole pattern  20  through which bolts extend from the peripheral edge of the air bladder  13 . The interface between the peripheral edge of the upper end plate and the air bladder  13  is provided with a suitable seal or sealing material to provide an air-tight interface. An upper mounting ring  21  is bolted to the lower inside face of the upper end plate  14  with bolts  22  inserted through the upper face of the upper end plate  14  into tapped holes in the upper mounting ring. The upper mounting ring  21  has a center opening  24  from which an attached guide rod  23  extends. As best seen in  FIGS. 6 and 7  the guide rod is welded at its upper end to the upper mounting ring  21 . The guide rod  23  is provided with an axially elongated through slot  25  to provide a guide and stop function as will be described below. Slot  25  also vents air to and from the blind bore  26  in the guide sleeve  28  described below. 
     Turning now to the lower end of the stroke control apparatus and referring also to  FIGS. 4-6 , the piston rod  17  (no longer acting as such) is provided at its upper end with an axial blind bore  26  for receipt of the guide rod  23 . The piston rod  17  thus becomes a guide sleeve  28  for axial movement of the guide rod  23 . The upper end of the guide sleeve  28  is provided with diametrically opposed holes  29  for receipt of a cross pin  27  which guides and, in part, limits the axial movement of the guide rod  23  within the bore  26  of the guide sleeve  28   
     A lower mounting ring  31  is secured to the guide sleeve  28  formed in the piston rod. The lower end plate  32  (from the air cylinder  12 ) is bolted to the lower mounting ring  31  with a circular pattern of bolts  33  extending upwardly through the end plate  32  and into tapped holes in the lower mounting ring  31 . A large diameter cylindrical stop sleeve  34  is welded or otherwise secured to the upper surface of the lower end plate  32  on the center axis of the apparatus. 
     The lower end of the guide sleeve  28  retains the lower end of the air cylinder piston rod  17  which is provided with a pair of parallel opposite flats  35  through which is provided an axially perpendicular bore  36  for pivotal connection to a suitable clevis or other pivotal mounting arrangement (not shown). 
     The outer peripheral edge of the lower end plate  32  is provided with a circular bolt hole pattern  37  for bolted connection to the lower end of the air bladder  13  in a manner similar to the upper end described above. The interface, of course, must also provide an air-tight seal. In the arrangement of components described above, the upper end of the stroke control arrangement includes the slotted guide rod  23  positioned axially in and attached to the upper mounting ring  21  and thus secured to the upper end plate  14 . The lower end of the guide and stroke limiting arrangement comprises the guide sleeve  28  secured to the lower end plate  32  and lower mounting ring  31  and a large diameter cylindrical stop sleeve  34 . The upper and lower portions of the guide arrangement are connected by the cross pin  27  which can move within the elongated slot  25  as the air bladder  13  is pressurized and depressurized to, respectively, extend and retract the air bladder actuator  11 . More specifically, maximum extension of the actuator by pressurizing the air bladder  13  is controlled by the cross pin engaging the bottom (lower end) of the guide rod slot  25 . Retraction of the air bladder  13  to its compressed state is limited by contact of the upper edge of the stop sleeve  34  with the underside of the upper end plate  14 . When this collapsing contact occurs, the cross pin  27  nests in semi-cylindrical recesses  40  in the bottom face of the upper mounting ring, but remains spaced slightly from the upper axial end of the slot  25 . An assembly of the retrofit internal guide and stroke limiting arrangement is shown in  FIG. 5  without the air bladder  13 . To reduce friction and facilitate relative axial movement between the guide rod  23  and the guide sleeve  28 , a suitable bearing sleeve  38  is preferably inserted axially into a counterbore  41  in the blind bore  26  of the guide sleeve. A manganese bronze/graphite hushing is one suitable type of bearing sleeve  38 . 
     In  FIG. 8 , there is shown an air bladder actuator of the present invention which is newly manufactured, rather than utilizing parts of an air cylinder actuator of the type shown in  FIG. 1 . In the  FIG. 8  construction, the upper and lower end plates  42  and  43  are of new construction. The upper mounting ring  44  and the guide rod  45  are of a unitary construction, machined from a casting or other steel piece. Similarly, the lower mounting ring  46  and guide sleeve  47  are also of unitary construction, machined from steel stock or a casting as well. The upper end plate  42  is bolted directly to the upper mounting ring, as in the previous embodiment. Similarly, the lower end plate  43  is bolted to the lower mounting ring  46  that carries the integral guide sleeve  47 . As in the previously described embodiment, the guide sleeve  47  carries a bearing sleeve  48  in a counterbore  50 . 
     Otherwise, the air bladder actuator of new construction, shown in  FIG. 8 , operates identically to the previously described retrofit embodiment.