Patent Application
20080121134
This invention relates to model railroads, and specifically to a model railroad truck having polymer springs therein.
Trucks that are used on model railroad rolling stock are scaled-down versions of prototypical railroad trucks. Although the framework for some trucks are formed as a one-piece structure, most trucks used by serious model railroaders include a separate truck bolster and spaced-apart side frames, wherein the bolsters are held in the side frames by means of springs, which allow a side frame to move torsionally relative to the bolster and to the other side frame. Wheel sets for each truck, including an axle having a wheel at each end thereof, are contained within journal boxes, which are located in the side frames. The flexible nature of the multi-piece truck allows the wheel sets to follow irregularities in the track, thereby maintaining the truck, and in turn, the rolling stock, on the track.
Known flexible trucks are quite difficult to assemble because the springs, which hold the truck elements together, are essentially free-floating, i.e., they are not secured to either the bolster or the side frame, and are usually captured to prevent lateral movement of the springs by protrusions which extend from the bolster and side frames. The springs used in both prototypical and model railroad trucks are usually coil springs, which extend between the end of a bolster and a truck side frame. In some instances, leaf springs may be used in prototypical trucks. Coil springs used in model railroad trucks are typically less than 0.16 cm in diameter and approximately 0.3 cm in non-compressed length. They are most difficult to handle. Although the use of a specialized pics may assist a model railroader with the insertion of springs into a truck assembly, the assembly of a conventional truck still requires that each individual spring be placed between the bolster and side frame. Generally, four springs are provided, two associated with each end of the bolster. Such assembly does not lend itself to any type of automation, and further, requires delicate manual assembly of the truck assembly, a task which produces stress in the hands and eyes of the assembly worker, and also results in increased manufacturing costs. Examples of a truck and an assembly technique which eliminate some of these concerns are found in U.S. Pat. No. 5,768,999 for Model Railroad Truck, granted to Edwards on Jun. 23, 1998, and U.S. Pat. No. 5,832,837 for Method of Assembling a Model Railroad Truck, granted to Edwards on Nov. 10, 1998.
Springs as provided on model railroad trucks provide for torsional movement of a truck side frame relative to a truck bolster, but do not really compress to provide cushioning for the rolling stock to which they are mounted. Torsion from side-to-side of a truck is important to enable the truck to pass over uneven trackwork, frogs and switch points. One solution used is to provide wheel sets with larger-than-scale flanges on the wheels, however this is highly objectionable to the serious model railroader. Another problem inherent in conventional sprung trucks is side frame toe out, which can actually lead to derailment.
Perhaps the most serious objection to the use of discrete springs in model railroad trucks is that the springs are not to scale. A prototype truck may have two or more large coil springs, or plural leaf springs, located between the bolster and the side frame, however, such springs are massive, and likely have a cross section of between two and three inches. The coil springs used on models are much finer, and, if converted to prototype scale, would have a diameter of less than half an inch, and would be non-functional in a prototypical world at this size.
A truck for use on a model railroad car, in association with plural axle/wheel sets, includes a left truck side frame and a right truck side frame, each having a bolster receiver therein; an elongate bolster extending between said right frame half and said left frame half, wherein each end of said bolster is received in said bolster receiver of a truck side frame; and a polymer spring member received in each of said bolster receivers between a bottom surface of said bolster receiver and a bottom surface of a bolster end for (I) retaining the bolster in the bolster receiver, and (2) allowing limited torsion of said left truck frame and said right truck frame relative to one another and to said bolster.
An object of the invention is to provide a model railroad truck which has a prototypical appearance, but which does not require the use of discrete springs between a truck bolster and a truck side frame.
A further object of the invention is to provide a model railroad truck which contains minimal components.
These and other objects and advantages of the invention will become more fully apparent as the description which follows is read in conjunction with the drawings.
The truck of the invention includes a three-piece frame having a pair of axle/wheel sets contained therein. In place of the convention coil springs, normally used to provide for torsional movement of the frame members relative to each other, a molded polymer spring member is provided, which provides for a torsion suspension. The torsion suspension provides reliable tracking by an exerting equal downward force on all wheels, even when traveling over uneven track-work, switches and frogs. With torsion suspension, a more prototypical wheel may be used, having wheel flanges which are more scale-like in appearance.
Referring initially to
A pair of axle/wheel sets 26, 28 are provided, wherein the ends of the axles are received in journals in the truck side frames. When the truck of the invention is assembled and installed on a model railroad car, and a load applied to bolster 18, the load is evenly transferred through the truck side frames to axle/wheel sets 26, 28.
The construction of the truck of the invention, while very different from conventional spring-containing model railroad trucks, provides for characteristics much like those of traditional spring-containing model railroad trucks, which allows for passage of a truck over an uneven section of track, because the truck side frames are able to flex relative one another, thus curtailing the incidence of derailments.
To maintain a prototypical appearance, “springs” 22 are integrally formed with spring member 20, which is formed by injection molding. Thus, the difficult fabrication step of installing coil springs in the trucks is eliminated, and the integrally molded springs 22 may be sized to be precise scale models of the prototypical springs found on full-scale railroad rolling stock.
One material which has been found suitable for fabrication of polymer spring member 20 is a material known as Sarlink® 3170, produced by DSM products. Although the product is available in a variety of durometer ratings, a durometer rating of 70 has been found to be particularly well suited for practicing the invention. The selection of a polymer for the sping member requires selection of a polymer having minimal changes in hardness with temperature changes and resistance to petroleum lubricants which may be used on the axles and wheel of the model railroad truck.
The truck of the invention provides improved rolling characteristics, more prototypical appearance, fewer parts and quicker assembly, which assembly may be accomplished by mechanical devices rather than by manual manipulation.
Although a preferred embodiment of the invention has been disclosed herein, it should be appreciated that further variation and modifications may be made thereto without departing from the scope of the invention as defined in the appended claims.
