Railcar having cold formed center sill with stiffness enhancing structure

A railcar comprising: a plurality of truck assemblies, each truck assembly having at least one wheel an underbody supported on said truck assemblies, said underbody including a cold formed center sill extending substantially the length of said railcar, wherein said center sill includes a top wall, a pair of side sections joined to the top wall by a pair of upper curved sections, bottom sections coupled to the side sections through curved connecting sections, wherein the center sill includes an upwardly extending stiffening longitudinal rib centered within the top wall.

BACKGROUND OF THE INVENTION

Field of the Invention

We, Douglas Jenkins and Gregory Josephson have developed this invention which relates in general to railroad cars and more specifically, to a cold formed center sill and its method of manufacture.

Background Information

The center sill is the primary structural member of the underframe of a rail car, and has been called the backbone or spine of the car body. A railcar center sill is subjected to the buff and draft forces created during operation of the rail car and generally extends as a continuous member along the length of the car body.

Historically, center sills have possessed many different cross-sectional configurations depending on the type of rail car and other considerations. One common configuration is the C center sill10, the profile of which is shown inFIG. 1. Another historically common design is the hat or Z center sill20, the profile of which is shown inFIG. 2. The Z designation was derived from the shape of the two components that were known to be coupled to form the structure.

Regardless of its particular shape, many prior art center sills were fabricated together from two or more hot formed sections in labor intensive processes. These historical hot formed processes yielded deviations in the straightness or acceptable tolerances of the center sill being formed that often resulted in further physical steps being needed to finish the center sill unit and conform it to acceptable tolerances in camber, sweep and twist to be suitable for use in a railroad car. The traditional welded center sill is an inherently heavy structure due to its design and fabrication technique.

In the 90s, attempts were made to address the deficiencies of the prior art center sill and a cold formed center sill30was developed as described in U.S. Pat. Nos. 7,478,599, 6,769,366 and 6,119,345 which are incorporated herein by reference. The cold formed center sill30disclosed therein has been successfully utilized since around 1996 and has yielded significant advantages. A conventional commercial cold formed, specifically cold rolled, center sill30profile is shown inFIG. 3.

Despite the acceptance of the conventional cold formed center sill30there were concerns raised about the inherent stiffness of the cold formed product as a whole. One theoretical proposal for addressing this was the inclusion of a pair of longitudinal inwardly extending stiffeners in a configuration of a cold formed center sill40shown inFIG. 4.

The proposed cold formed center sill40profile was also similar to the conventional and commercially available cold rolled shape30but further includes a pair of inwardly disposed ribs50rolled out of the two side sections for webs52of the center sill6c. The inwardly directed longitudinal ribs50were designed to serve as stiffeners for the elongated center sill and were intended to be cold formed during the rolling process. The proposed center sill40includes a top wall54which is oriented at 90 degrees to side sections52by a curved portion55having an approximate radius, for example, of 15/16 inch and the like. The ribs52include inwardly extending connecting portion56of a length less than an inch and have a flat internal wall57to rigidize the center sill. The connecting portions56are also worked hardened as are curved portions55. The bottom of the center sill includes a pair of partial horizontal bottom sections58integral to side sections52by curved sections59. The bottom sections define longitudinal bottom opening60along the center sill6c.

The cold formed center sill40design with the inward extending ribs50did not prove to be commercially successful or readily producible. In theory this design yielded improved stiffness, but the costs of production creating the rolling mills for this shape were too high for commercial feasibility outweighing the increase in theoretical operation.

Thus there is a need for cold formed center sills with stiffness enhancing structures that may be manufactured in a cost effective manner so as to be commercially acceptable and railcars incorporating the same.

SUMMARY OF THE INVENTION

The object of the present invention is achieved according to one embodiment of the present invention by providing a railcar comprising: a plurality of truck assemblies, each truck assembly having at least one wheel an underbody supported on said truck assemblies, said underbody including a cold formed center sill extending substantially the length of said railcar, wherein said center sill includes a top wall, a pair of side sections joined to the top wall by a pair of upper curved sections, bottom sections coupled to the side sections through curved connecting sections, wherein the improvement comprises an upwardly extending stiffening longitudinal rib centered within the top wall.

The features that characterize the present invention are pointed out with particularity in the claims which are part of this disclosure. These and other features of the invention, its operating advantages and the specific objects obtained by its use will be more fully understood from the following detailed description and the operating examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 5, there is illustrated a railroad gondola car60for carrying commodities such as coal, gravel and the like and having an underbody carried by opposed truck assemblies62. The underbody of the railroad car60of the invention includes a continuous cold formed center sill70with stiffness enhancing structures according to the present invention and which is extending substantially the entire length of the car60:

A railcar body80is attached to the underframe. As will be apparent from the following description, the cold formed center sills70of several embodiments of the invention provide significant advantages over prior center sills and contribute to a lightweight, economical car design. Although the center sills70of the invention are shown with reference to the gondola car ofFIG. 5by way of illustration, it is within the scope of the invention to use the center sill70herein disclosed with any type or design of railcar in which the advantages of the invention are desired. Essentially any railcar having a through center sill (not a stub sill) could utilize the center sill70of the present invention.

The cold formed center sills70of the present invention with stiffness enhancing structures will generally increase in weight over a cold formed center sill30of the same grade and thickness and profile not having the stiffness enhancing structures, however the benefits of including the stiffness enhancing structures outweigh the extra weight of the sill70itself. Increasing the stiffness of the center sill70over an analogous sized sill30will allow the center sill70of the invention to absorb more of the coupler load and uniformly transfer this higher load to the next railcar, thereby minimizing the forces to be carried in the extraneous structural members of the railcar60like the side sill and other structures, thereby allowing for overall weight reduction to the car due to substantial weight savings in extraneous components.

InFIG. 6is illustrated the first embodiment of the cold formed center sill70including stiffness enhancing structures of the invention. The center sill70is formed from suitable steel by a cold forming process. The process may be a cold rolling process through a series of rolling mills, or alternatively the shape may be made in two pieces joined together with each steel member being formed on a hydraulic brake or press. The center sill70may thus be formed in a generally rectangular configuration from one or two flat one-piece plate or coiled sheet of steel and the center sill70is continuous along its length. The center sill70is formed by bent sections created in the cold forming process from a material having a thickness of between ¼ up ¾ ″ with ⅜ inch to ⅝ inch being preferable, and 0.4-0.5″ being most preferred. The center sill70according to this embodiment includes an upper top wall82and a pair of flat side sections or webs84, each of generally constant thicknesses.

The top wall82and pair of side sections or webs84are joined together at right angles by upper curved sections86being formed about a common radius such between about 0.75 and 1″ radius. The bottom sections88of the center sill70are inwardly formed horizontally at right angles to the side sections84through curved connecting sections90being of constant radius between about 0.75 and 1″ radius. The bottom sections88terminate in a pair of upright internal flange portions92extending upward and being joined to bottom portions by curved sections94of constant radius. Spaced between the internal upright flanges is a longitudinal opening100through which access to a apace within the center sill70is provided. By way of example, the bottom sections88forming the bottom portions of the center sill70may each extend approximately 4 inches from the side sections84with the opening100sufficient to receive a huck gun therein for assisting railcar manufacturing. The center sill70is preferably formed of steel having an average yield strength throughout its length of 50,000 to 80,000 PSI. The stiffening structures in the center sill70of the present invention more easily accommodates use of 50,000 PSI to be utilized, however the use of higher PSI steels can yield great weight savings for the overall railcar60. For other reasons the 50,000 PSI is often generally preferred by customers in the industry, although weight savings is also desired, so the selected PSI of the steel remains a tradeoff.

The curved sections86,90,94are cold worked numerous times during the cold rolling process. As a result, the material is cold hardened and strengthened at sections as compared to its original unformed state. The resulting cross section does not require thicker sections or added material as in the prior art C shaped and Z shaped center sills10,20and provides a high-strength member.

The key feature of the present invention is the provision of an outwardly or upwardly extending offset or stiffening longitudinal rib centered within the top wall82. The offset includes a left and right transition segment96extending to a central flat land98generally aligned with the opening100and wider than the opening100. The offset is a stiffening structure that increases the overall height of the center sill70to 13.938″ and the overall density of the center sill70is 82.3 lbs/ft with 0.5″ thickness steel. This compares with 78.4 lbs/ft for a conventional cold rolled center sill30of 0.5″ thick steel of 12.938″. The offset increases the bounded area or envelope of the center sill70that tends to improve resistance to buckling. For example in a 0.4″ thick steel version of this embodiment of the present invention the envelope or bounded area is 18.9503 square inches and the conventional envelope of the same thickness (without the stiffener or offset) is 18.7583 square inches. The offset yields, for this particular configuration, greater than 1% increase in the bounded envelope and an associated increase in resistance to buckling forces.

The center sill70of the present invention was compared with a prior art cold formed center sill30and a C center sill10and a Z Center Sill20. Each center sill70,30,10,20was analyzed using 1″ tetrahedronal elements in ANSYS brand software. Remote displacements were placed at each end of the center sill70,30,10,20and a downward force of 1000 lbs was applied to the top surface. The maximum stress and maximum deflection are presented in the table below for each center sill70,30,10,20, along with the weight per foot.

As noted in the analysis above, the deflection of the center sill70of the present invention is less than that of the standard cold formed center sill30and is actually better than the conventional C center Sill10or Z Center Sill20of similar thickness (0.5″ plate). Additionally the weight per foot is less than the conventional C Center Sill10and Z Center Sill20, although not as light as the conventional cold formed center sill30. The center sill70of the present invention still significantly reduces the weight of the overall railcar60. Additionally the profile of the present invention can be efficiently formed and yields the improved results described above.

A second embodiment of the center sill70including stiffness enhancing structures of the invention is shown inFIG. 7. The center sill70is formed from suitable steel by a cold rolling forming process, such as cold rolling or cold pressing. Cold pressing would be using two steel members in a hydraulic brake or series of brakes. The center sill70is formed by bent sections having a thickness as discussed above. The center sill70includes an upper top wall82and a pair of side sections or webs84, each of generally constant thicknesses. The configuration exceeds the strength characteristics of the preceding embodiment for the same dimensions and material and is also preferably continuously formed from a one-piece coiled sheet or plate or as a two piece structure.

As with the first embodiment the top wall82and pair of side sections84are joined together at right angles by upper curved sections86being formed about a common radius. Similarly, the bottom sections88of the center sill70are inwardly formed horizontally at right angles to the side sections84through curved connecting sections90being of constant radius. The bottom sections88terminate in a pair of upright internal flange portions92extending upward and being joined to bottom portions88by curved sections94of constant radius. Spaced between the internal upright flanges92is a longitudinal opening100through which access within the center sill70is provided. The center sill70preferably possesses an average yield strength as discussed above.

Like the first embodiment of the present invention, a key aspect of the invention is the provision of an outwardly or upwardly extending offset or stiffening longitudinal rib centered within the top wall. The offset includes a left and right transition segment96extending to a central flat land98generally aligned with the opening100and wider than the opening100. The offset is a stiffening structure that increases the overall height of the center sill70to 13.938″.

The difference between the first embodiment and the second embodiment of the present invention is the inclusion of a pair of outwardly extending side offsets or stiffening longitudinal side ribs centered within each side wall84. Each side offset includes a top and bottom transition segment106extending to a central flat land108generally centered on the side wall84. The side offsets are stiffening structures that increases the overall width of the center sill70to 15.313″ (from a conventional width of 13.813″) and the overall density of the center sill70is 83.7 lbs/ft with 0.5″ thickness steel. The increased weight is offset by an increased stiffness to the overall center sill70of this embodiment. The stiffening structures of this embodiment yields greater than 3% increase in the bounded envelope and an associated increase in resistance to buckling forces.

A third embodiment of the center sill70including stiffness enhancing structures of the invention is shown inFIGS. 8A and 8B, with the common features not described in detail again. In this embodiment the top offset is formed across the entire top82of the center sill70and mimics the shape of a center sill shroud with the transition elements116extending from a modified upper curved section86′ to a top central curved section114. The upper curved sections86′ are modified in that each couples a side84to the transition elements116and not to a perpendicular member as in earlier embodiments. Here the increase in bounded area may be about 5%. The weight of this design with 0.5″ steel is 107.414 lbs/ft. An alternative center sill70to this third embodiment is shown inFIG. 8Band the difference is to eliminate the internal flanges92and the associated coupling94for weight savings, dropping the weight per foot to 103.308 lbs/ft for a 0.5″ thick design:

A fourth embodiment of the cold formed center sill70of the present invention is shown inFIG. 9. In the further embodiment the stiffening structure is an offset extending across the entire top82as shown including transition elements116from modified corners86′ to the flat central land98. This center sill70further includes a reinforcing plate120welded in the interior only adjacent the draft arm ends and extending for a few feet to stop about at the floor intersection.

In all of the center sills70of the present invention the top surface of the center sill is above the top surface of the draft arms due to the stiffening offset structure. Conventionally in the prior art center sill structures the top surface of the center sill is aligned with the top surface of the draft arm. The reinforcing plate100in the fourth embodiment is aligned with the top surface of the draft arm and can convey forces down to the floor intersection. The stiffening structures of this fourth embodiment yields greater than 2-4% increase in the bounded envelope and an associated increase in resistance to buckling forces.

The above discussion illustrates that the cold formed center sills70of the present invention offer significant advantages over the prior art center sills10,2030or40without detrimental drawbacks. It will be apparent to those of ordinary skill in the art that various changes may be made to the present invention without departing from the spirit and scope thereof. Consequently, the present invention is intended to be defined by the appended claims and equivalents thereto.