Interface - The Journal of Wheel/Rail Interaction

VEHICLE SUSPENSIONS

Design Considerations to Meet the M976 Specification
July 21, 2004

Thomas berg, vice president - Engineering and Product Development at Amsted Rail Group - ASF-Keystone Products outlined the five primary components of the ASF Motion Control™ system that give the truck its M-976 levels of performance:
• Pennsy AdapterPlus elastomer steering pads allow improved wheelset steering and radial alignment, and reduced rolling resistance.
• Tuned suspension improves vertical ride quality and reduces hunting.
• ASF Spring Control long-travel, constant-contact side bearings control hunting and allow better load distribution through curves and in dynamic curving.
• Super Service Ridemaster variable damped friction shoes improve warp stiffness of the truck and improve stability. They also improve curving and high-speed stability.
• ASF patented lightweight, tight-tolerance, one-piece castings provide better alignment from side frame to side frame and bolster to bolster end, and are lighter by about 1100 pounds per car set.

"Typically trucks either curve well or have good high-speed stability," Berg said. "It was a challenge to design a truck that accomplished both."

To do so, ASF tuned spring damping rates to match the car type and capacity. This, along with steel spring side bearing designs that provide consistent pre-load, provides improved vertical ride quality and high-speed stability. The M-976 compatible design also has reduced rolling resistance by about half—from about 0.6 for conventional trucks to about 0.3 for the Motion Control™ truck.

The new specification also requires that maximum vertical accelerations (pitch and bounce) remain less than 1g. The new ASF design generates just over 0.5g maximum, while using as much of the suspension as possible to improve ride quality, but remain below the 95% maximum travel allowed by the spec.

As part of the industry's ongoing development, field performance will be monitored with a view toward identifying performance-based service limits on products. "We need to study what these trucks do in the real world to determine how long they will maintain their improved performance characteristics," Berg said.