Railway rolling stock – Trucks – Bogie
Reexamination Certificate
2001-01-29
2004-02-10
Lavinder, Jack (Department: 3683)
Railway rolling stock
Trucks
Bogie
C267S003000, C267S209000, C105S198400
Reexamination Certificate
active
06688236
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to “three-piece” railroad car trucks, and more particularly to the four friction wedges that interface the bolster with the side frame and provide suspension damping and warp stiffness. Warp friction moment, the measure of interaxle shear moment necessary to produce truck warp, is the primary characteristic that governs truck warp stiffness, and it is a characteristic that three-piece trucks are known to be deficient in. Damping force levels, on the other hand, have not been a problem to achieve in any magnitude desired, but are a problem if they are too low or too high. The present invention teaches the desired relationship between friction wedge angle, friction coefficient, wedge spring force, and wedge width to provide a friction wedge that will simultaneously produce a very high to infinite warp friction moment with a moderate to low damping force.
By increasing the warp friction moment, higher interaxle shear stiffness, or truck warp stiffness can be achieved. Warp stiffness, is the primary characteristic of two axle trucks that determines high-speed stability and heavy axle load curving performance. Static warp friction moment, commonly described as the warp friction moment, is the friction force couple, produced primarily by the friction wedge, in resistance to truck warp forces or interaxle shear forces. It is called the static warp friction moment, because the resistance moment produced by the wedges is limited by static friction. It is the objective of the present invention to increase the warp stiffness of the three-piece truck by increasing the warp friction moment through an optimization of the friction wedge design.
In the present invention, by simultaneously equating the warp friction force with the maximum interaxle shear force, and the damping force to a percentage of the sprung weight, it is possible to achieve a friction wedge design that both resists truck warp, and maintains a safe level of suspension damping. The use of a pair of simultaneous equations enables the design engineer to produce a friction wedge design based on the maximum warp friction moment and damping rate desired, rather than on the basis of the damping rate alone. The result of the equations is a set of parameters for the complete design of a friction wedge and a side spring optimized for warp friction and damping.
BACKGROUND OF THE INVENTION
In North American freight railroad service, conventional three-piece freight car trucks, having two wheelsets, have evolved to satisfy a variety of important operating and economic requirements. Among other requirements, they must be capable of safely supporting, and equalizing very high wheel loads over a wide range of track conditions while delivering a high level of economic value to the railroads that use them. In addition to those basic criteria, the trucks and their parts must be interchangeable throughout the system of interconnected railroad networks. The three-piece trucks in service today have, to a large extent, met these requirements, because their general designs are simple, flexible, durable, and reliable. However, in this evolutionary process, a major aspect of truck design for performance efficiency has been largely ignored, design for warp friction moment.
When a conventional three-piece truck encounters sufficient energy in the course of its normal use, usually due to high-speed operation, the wheelsets are forced to move laterally relative to the track and relative to one another causing the instability known as “truck hunting”. Truck hunting is undesirable, because it causes high lateral forces to be imparted to the rail vehicle and its lading, and because it produces increased drag on the locomotive, resulting in reduced efficiency. Likewise, when a conventional three-piece truck encounters a curve in the normal course of its use, the wheelsets are often forced to move laterally relative to one another resulting in a condition known as “truck warp”. Truck warp is undesirable, because it causes a high angle of attack to arise between the leading wheelset and the rail, resulting in high rates of wear on the rails and wheels. Whether they are a result of high speed or curving, truck hunting and truck warp are generally characterized by a lateral displacement of the wheelsets relative to one another, and a change of the square relationship of the side frames relative to the bolster into an angular relationship.
Testing of conventional three-piece freight car trucks involved in heavy axle load derailments has shown that a large proportion of the interaxle shear stiffness that governs their performance is attributable to the side frame to bolster connection. However, current designs of this connection have an inherent problem in that they only provide resistance to unsquaring movements between the side frames and bolster up to the limit of the coulomb friction force that binds these connections. Recent theoretical modeling, and laboratory testing have confirmed that the warp friction moment is the critical determining factor in the performance of the three-piece truck.
The side frame to bolster connection design of three-piece trucks is generally characterized by a right triangle shaped friction wedge in contact with and contained by a pocket in the bolster on one side, a vertical surface of the side frame on another, and a spring on the third side. The connection is comprised of three load bearing interfaces: the Spring Seat Surface, the Slope Surface, and the Column Surface. The wedge surfaces are oriented in the shape of a right triangle with the spring seat and column surface oriented at a right angle to each other, and the slope surface oriented at an acute angle to the column surface. The wedge is oriented with the column surface vertically to allow sliding motion of the bolster relative to the side frame due to dynamic forces of the rail vehicle body. The wedge slope surface bears on the bolster pocket slope surface, which acts to direct the force of the spring from the spring seat surface into the column surface. As a result of the wedge configuration and orientation, a force balance is formed on the friction wedge, at the three interfaces, that is governed by the relative position and movement of the bolster to the side frame.
Three different force balances are possible: the spring Compression Stroke force balance, the spring Decompression Stroke force balance, and the truck Warp Action force balance. The compression and decompression stroke force balances are the force balances that describe the coulomb damping forces in the three-piece truck, and they have been used for many years by design engineers to design friction wedges for vertical damping. These two force balances are governed by the wedge angle, the spring force, and the coefficients of friction between the materials of the wedge and the column and slope surfaces respectively. The warp action force balance describes the forces that act on the wedge under interaxle shear force conditions, and it gets its name from the interaxle shear or truck warp forces that generate the wedge forces. Under warp action, the friction forces that otherwise act in opposite directions, act upward in the same direction, and bind the wedge between the column and side frame up to the limit of the static friction forces at those interfaces.
The warp action force balance that describes the warp action forces on the wedge is new, and has neither been described in the prior art nor publication literature. It was discovered through a parameter effect analysis of the wedge force balance parameters. The objective of the analysis was to determine the effect on the damping force of the governing parameters: wedge angle, friction coefficient, and spring force. The analysis revealed the exponential nature of the damping force to the wedge angle and friction coefficient. The association of this fact with the fact discovered in the derailment investigations that trucks with smaller wedge angles were much less likely to derail, lead to the discovery
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
King Bradley
Lavinder Jack
Standard Car Truck Company
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