Patent Application
20060272908
Braking of a railroad freight car is accomplished with pneumatic cylinders acting through a series of mechanical linkages to force brake shoes against the car wheels as they rotate. Each brake shoe is mounted in what is called a brake head. A pair of brake heads are mounted on a brake beam, one brake head at each end of the brake beam so as to provide a brake shoe for each wheel of a wheel set. Brake shoes can wear quickly and are designed to be removable. A brake shoe is retained in the brake head by means of a spring steel piece called a brake shoe key. The key acts as a spring and tightly holds the brake shoe against the brake head. A brake shoe is installed by driving the key through adjacent openings in the shoe and head.
The configuration of the key is an industry standard, defined by AAR S-376, which has been in place for over twenty years. However, there are several problems with the design. In order for the key to properly retain the shoe, it must be driven all the way into the brake head, until the tang contacts the head. However, once a car is in service and a brake shoe needs to be replaced, removal of the key is difficult due to lack of access. To remove the key, one must pry it out by the tang. But the key itself is in an awkward position. It can be reached only through an opening in the side frame of the truck. If the key has been properly installed, i.e., it has been driven all the way in, it is difficult to get a lever under the tang for removing the key.
In order to avoid this problem, railroad workers have developed the practice of not driving the key all the way into the head. While this makes it easier to remove the key at a later time, the brake shoe is not properly retained in the head and there is a risk the shoe may be lost in service. The curved portion of the key that functions to hold the brake shoe to the brake head is not centered relative to the brake shoe's mounting lug. The resultant force holding the shoe in place is therefore lower than it should be. Furthermore, the key in this situation inter-faces with the brake shoe's mounting lug in an unintended, off-center location, which might contribute to the failure of either part.
One solution to this problem is to make the brake shoe key longer. This would allow it to remain part way out of the head for easy removal while also allowing for the correct interface between the key, the shoe and the head. But merely lengthening the key alone would add another possibility for improper installation of the key. It could be driven in too far, resulting in the same undesirable interface between the key and the shoe.
Although the tang on the current S-376 standard key does function as a stop to position the key correctly for proper retention of the brake shoe, it has the unintended consequence of making it difficult to remove correctly-installed keys. Other alternatives have been proposed without success. These alternatives have focused on changing the tang configuration and the interface between the brake shoe key and the external end of the brake head. One of these alternatives is provided in the S-376 standard. It changes the tang design. The stop in this design will not function correctly because many brake heads have no surface against which this type of tang may abut. Another recent proposal would make the tang a “C” shape. This would work as a stop but it has the drawback of not providing a solid surface on the key for striking with a hammer during installation. A further proposal includes a small stop similar to that in the present invention but intended to abut the exterior end of the brake head. This will not work because in the fully installed position the end of the key floats in the brake head opening, not touching either side of the opening. Field surveys have also revealed that the straight tang design needs to be improved since there is a tendency for the metal pry bar to slip during removal of the keys that may lead to injury.
The present invention provides a brake shoe key which solves these problems.
A brake shoe key for railroad brake shoes has a shank with upper and lower legs and a tang at the end of the upper legs. A mechanical stop is formed on the upper leg so as to be engageable with a strut of the brake head to ensure that the key is driven to the proper distance to properly retain the shoe while at the same time leaving enough room between the tang and the brake head to facilitate removal of the key at a later time. A bend is formed on the upper leg to act as a visual indicator that the key has been driven to the proper distance. The end of the tang is bent 90 degrees to secure the pry bar and prevent it from slipping during removal of the keys.
The brake shoe key of the present invention is illustrated generally at 10 in
There is a tang 20 formed at the top of the upper leg 12. Preferably the tang is a folded-over portion that permits driving the key with a hammer and withdrawing it with a prying tool. The positions of the stop 18 and the tang 20 in relation to the knee 16 is important, as will be explained below. The key is completed by a foot portion 22 that includes a plurality of steps or corrugations 24. The corrugations will engage the bottom edge of a brake head and help retain the key in the fully installed position. A bend 26 is also formed on the upper leg to act as an indicator showing that the key has been installed properly when the bend 26 is no longer visible from the side. A small flange 28 is formed on the free end of the tang 20. The flange serves the purpose of securing a metal prying tool in place and preventing it from slipping off the tang during the removal of the key. This flange 28 is designed specifically to address the safety issue of pry bars slipping off during removal of the keys.
The brake shoe 46 includes a backing plate 48 to which the brake shoe pad 49 is attached. The pad is made of suitable friction material. The backing plate 48 has a central mounting bridge or lug 50 with upper and lower slots 52 and 54 formed therein. When the shoe 46 is placed on the brake head 30 the lug 50 fits into the well 36 and the backing plate 48 engages the central struts 42, 44. This makes the brake shoe ready for retention by the brake shoe key 10.
The key 10 is inserted into the keyway 34 and driven downwardly. The foot 22 goes through the slots 52, 54 of the lug 50. The key is driven into the keyway until the stop 18 engages the upper central strut 42, as seen in
The present invention recognizes that the internal features where the head, the key and the shoe interface are much more uniform among the various commercially available designs than are the external features against which any tang-type stop must abut. For any key to work it must make contact at these interior surfaces in the manner shown in
While a preferred form of the invention has been shown and described, it will be realized that alterations and modifications may be made thereto without departing from the scope of the following claims.
