Railway rolling stock – Trucks – Bogie
Reexamination Certificate
2004-01-23
2004-11-16
Le, Mark T. (Department: 3617)
Railway rolling stock
Trucks
Bogie
C105S197050, C105S207000
Reexamination Certificate
active
06817301
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a railroad freight car truck suspension which is used to carry a freight car over the rails of a railroad, and more particularly to a means for mitigating the detrimental effects of using a conventionally designed railroad freight car truck at both relatively high and low speeds, the high speed being in excess of 80 kmh (kilometers per hour) or 50 mph (miles per hour) and the low speed being less than 40 kmh or 25 mph in curves where excessive yaw is a critical problem.
BACKGROUND OF THE INVENTION
A typical railroad freight car is provided with a pair of trucks located at opposite ends of the freight car to support its body. Such a truck is provided with a pair of wheelsets each of which comprises an axle, a pair of spaced wheels and a tapered roller bearing assembly mounted at each axle end, and the truck is pivoted to the body of the freight car to permit its trucks to negotiate a curve. A conventional truck, referred to as a “three piece truck” includes a pair of longitudinal side frames with a pair of wheelsets extending between the side frames, at opposite ends of the side frames. By “longitudinal” is meant the direction in which a truck is translated along rails, or the direction in which the rails extend. The wheelsets are journalled to rotate about a horizontal axis to allow the truck to roll along rails. The side frames are interconnected by a bolster that is mounted to each side frame by inserting the bolster through a through-window known as a “window opening” in each side frame. The central lateral axis of the bolster in a freight car truck at rest, is essentially at right angles to the longitudinal central axis of a side frame. The bolster's ends are supported on a set of springs in each side frame, to accommodate vertical, and to a smaller extent, lateral loads, and the springs are seated within spring seats on the side frame. The bolster is pivotally connected to the body of the freight car to provide the necessary connection between the body and the truck. The bolster may be displaced vertically relative to the frames, depending upon the loading of the bolster, but lateral displacement of the bolster is limited by vertical ears known as “bolster gibs” projecting from the bolster. The interface between the bolster and side frame includes spring loaded wedges (“friction wedges”) which fix the longitudinal movement of the bolster, and, to a lesser extent, control the vertical and lateral and rotational motions between the bolster and the side frames.
Because the friction wedges permit the transmission of longitudinal forces and rotational forces and/or torsional moments from the side frames to the bolster, any difference in the magnitude of these forces at each end of the bolster will, when the resistance due to friction between the bolster and car body is exceeded, cause pivoting of the bolster in the horizontal plane. In addition to such movement of the bolster any imbalance in the magnitude of vertical forces exerted on the spring-supported ends of the bolster caused by a first pair of wheels on one side of a pair of wheelsets, on one side of the truck, will tend to unload the other end of the bolster which will move vertically relative to the second pair of wheels of the wheelset on the opposite side of the truck. This accommodation of vertical movement allows the truck to travel over track which is uneven and maintains a good load distribution between the four wheels of the truck.
Though the conventional truck side frames provides a very stiff longitudinal constraint which maintains the wheelsets parallel to one another the conventional design is ineffective in keeping the wheelsets aligned in a lateral direction in the horizontal plane. The imposed lateral loads generated between wheel and rail at a high speed above 80 kmh on straight track and lower speeds below 40 kmh on curved track tend to rotate the side frames about the ends of the bolster allowing misalignment of the wheelsets or truck warping.
First, the action at higher speeds: the problem is exacerbated when there is warping or an in phase yaw displacement in which the wheel sets remain parallel to one another but not perpendicular to the side frames. This in phase yaw displacement is commonly known as lozenging and results in two undesirable characteristics. Firstly, an unstable condition known as hunting can occur in which the yaw displacements occur in a continuous oscillatory manner excited by the action of the wheels against the rails. Such a motion promotes high wheel and rail wear, causes high shock levels to be transmitted to the rails and the vehicle body and can, in extreme cases, lead to derailment of the vehicle.
The second action occurs on curves. When the vehicle travels on curves of sufficiently small radius to cause the leading wheelset to come into flange contact with the outer rail the wheelset experiences a yaw torque which turns it toward the outer rail. This creates a very high angle of attack of the leading axle with the rail and it is well known that such high angles of attack result in high levels of wear and noise as well as creating high force levels and the possibility of derailment.
One solution to such lozenging has been to use trucks having a rigid H frame. In this type of construction the bolster and side frames are integrally formed so that relative longitudinal displacement (in the direction of the rails) between the side frames cannot occur. Such frames tend to be extremely rigid so that their ability to accommodate vertical movement between the axles is not very good, and it has been shown that such rigidity results in a relatively low critical velocity, that is, the velocity at which instability occurs is typically less than 80 kmh.
It has also been suggested to use two braces extending diagonally between the side frames and bolted and/or welded to each other at their intersection. This construction is effective in controlling instability and improving “curving” since the construction has a high warp stiffness and is not rigid; however, it is subject to failure due to fatigue resulting from vibration.
In North America and in other countries that follow the North American practices, the conventional three-piece freight car trucks in railroad freight service have evolved to satisfy a variety of important operating and economic requirements. Freight car trucks must be capable of safely supporting and equalizing very high wheel loads over a wide range of track and operational conditions while delivering a high level of economic value. The three-piece trucks in service today are being challenged by ever increasing demands for improved performance. Effective Jan. 1, 2003, this demand for better performance reached a new level when the Association of American Railroads (“AAR”) issued a new specification M-976-2002, “Truck Performance Specification For Rail Cars,” that sets the performance requirements for all freight car trucks. Most all current freight car truck designs are failing to meet all of the performance requirements of the new AAR specification. The main reason for the failure is the conflicting requirement for good vertical flexibility and high inter-axle shear stiffness or truck warp stiffness.
Freight car truck design requirement for the proper selection of suspension springs and friction dampers along with the proper selection of a higher than normally available interaxle shear stiffness was known in the early 1970's (see AAR Track Train Dynamics Program Phase I & II). In order to meet the vertical suspension requirements larger friction damping wedges with higher damping forces were developed (see U.S. Pat. No. 5,511,489 to Bullock, inter alia). In order to increase the inter-axle shear stiffness various additional structures have been added to the three-piece freight car truck. These attempts include a spring plank connecting the spring seats of the truck side frames (Weber Patents and List U.S. Pat. No. 4,483,253), directly inter-connecting the wheelsets to each other through a sub-frame (U.S.
Le Mark T.
Lobo Alfred D.
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