2. Field of the Invention
The present invention relates to improved railway car suspensions, and more particularly to improved means for stabilizing or dampening the load supporting spring suspension of a railway car so as to prevent the build up therein of vibration frequencies of objectionable amplitudes which can cause excessive swaying, rocking or bouncing of the rail car, especially of the new high volume rail cars, and can be dangerous when excessive.
It is well known that a railway car can be bounced vertically by several forces as the railway car proceeds down a railway track in operation. Most pronouned of these forces is the vertical bouncing produced when the wheels of the railway car pass over the rail joints of the track way. Other types of vertical forces can be imparted by objects on the railway track, or flat spots on the railway car wheel, etc.
It is this bouncing action that sets up forced vibrations in the spring suspension assembly of the railway car truck. This, in combination with the natural frequency of the springs of the railway car truck, determine the critical frequency of the car truck, and when the car truck is operated at speed at which this critical frequency occurs, an objectionable and dangerous bouncing action is set up in the spring suspension of the car truck. Even at speeds other than the critical frequency, it is desirable to minimize the forced vibrations incident to the car truck construction.
The earliest way to do this was to place the joints in the rails so that the rail joints on one side of the track are midway of the joints on the other side of the track. Since the bouncing by traveling over the rail joints are the main forces acting on the car truck, this minimized any vibrations incident to the track construction, and at this point one had to just make sure that the rail car truck was not operated at a speed to cause the critical frequency to be reached.
However, in addition to the spring vibrations incident to the vertical bounce of the car, there are other forced vibrations which are equally undesirable, such as, for example, the vibrations incident to the lateral swaying or roll of the car body, or the fore and aft lurching of the car body. All of these shock waves, and the forced vibration frequencies resulting therefrom vary in relation to the weight of the load, the center of gravity as effected by the density of such load, and the speed of operation. It was, therefore, found that the expedient of placing track joints on alternate sides of the track was not enough to provide a smooth riding suspension for a railway car. This was especially true when one considers the difference in weight between a loaded and an unloaded car, and now with the advent of the high volume or high-cube cars, the forced vibrations which could be set up by swaying or lurching of the car, and the effects of forced vibrations set up by the rail joints are even more undesirable.
2. Description of the Prior Art
Prior to the present invention, many remedies have been tried to provide additional dampening force, and thus minimize the undesirable effects of these forced vibrations. My own prior U.S. Pat. No. 2,873,691 entitled, "Stabilizing Structure for Railway Car Spring Suspension" discloses a system particularly adapted for removing objectionable forced frequencies by the utilization of friction dampening means, together with different length springs to provide a different springing effect for loaded and unloaded railway cars. Because the inner and outer springs used are of two different lengths, this is known in the art as providing two-stage springing. My prior art patent provided a satisfactory solution to the problem of how to provide a railway car truck suspension which would provide satisfactory operation without objectionable resonance, both in a loaded, and unloaded, railway car.
My U.S. Letters Patent No. 4,333,403 entitled, "Retainer Railway Car Truck Bolster Spring" also relates to this problem, and provides a more satisfactory way of holding the inner coil spring in relation to the outer coil spring.
However, as the need for increased efficiency made itself felt in the American railway industry, thus forcing the move to larger and larger volume box cars, and resulting in what is known as the high volume or high-cube car, this type of railway truck suspension was not adequate, as the additional height of the car made the truck suspension acutely susceptible to forces providing objectable roll during operation of the railway car.
Essentially, two operational problems are encountered in the movement of, for example, one hundred ton high volume covered and open top hopper cars. One of these is the tendency of the cars to rock excessively when loaded, and the other problem is the operation of these cars empty.
Attempts to provide additional dampening took two directions. The use of non-linear, variable, fixed springs to control vibration of these freight cars was attempted without success due to the lack of space, and the need to control coupler height.
Thus, the only other solution that was found satisfactory was to utilize addtional hydraulic dampening or snubbing devices. However, this solution is not satisfactory because it results in the spring deflection of empty cars being very small, causing the aforementioned excessive rocking, and the very heavy spring rates needed give an objectionable ride under partially loaded conditions.