Improving Truck Designs to Reduce Forces
Transmitted to Track
(continued)
To better control the stresses associated
with heavy axle loads, the industry developed and implemented
new standards for suspension systems on heavier cars. M-976
represents a general standard that is not car weight specific,
whereas the AAR S-286 standard, which applies to cars in
unrestricted interchange service with gross rail loads between
268,000- and 286,000-pounds, requires truck systems with
improved suspensions that meet the AAR M-976 performance
requirements. The S-286 standard became effective this year.
HAL
Testing
In the process of developing these new AAR standards, the
TTCI solicited and evaluated improved suspension designs
for bulk
commodity service. This was part of its HAL testing between
1999 and 2001. The results were positive. The five prototype
systems
demonstrated—three 315k- and two 286k-load designs—showed
a 50% reduction in dynamic loads and the amount of energy consumed
at the contact patch. Twist and roll, track perturbations, which
generate a side-to-side motion on tangent track, and carbody
roll were also reduced. Conventional trucks generated nearly
2g dynamic loads, while the improved suspensions generated about
0.6g loads, Berg said. "That generates less wear and
tear on the infrastructure."
Improved-suspension trucks reduced lateral forces and rolling
resistance at the contact patch from about 0.9 pounds per
ton per degree in the baseline trucks to under 0.5 for the
improved
trucks in a 12-degree curve, Berg said. "From an economic
standpoint, the effect that reducing rolling resistance has
on wheel costs is in the range of 10% to 20% per truck per
100,000
miles, depending on the routes and the amount of curvature."
