Advanced freight car truck program - Vehicle Track Systems Newsletter

Railway Age, Dec, 1995

Controlled tests

Automobile manufacturers currently use over-the-road data to run their transportation simulation shaker systems. Although the FDS recommended practice also requires over-the-road testing for new designs, an advantage of controlled testing is that it can provide a quick method for fine tuning a new system or revealing design weaknesses before a production vehicle is made. Another advantage of controlled test data is that it can be used to compare performance of systems developed at different times. Controlled tests evaluate ride performance at high speed on tangent track and when operated on tracks designed to excite twist and roll or pitch and bounce resonance in the autorack system. Impact testing is another controlled test regime. However, truck suspension does not affect the impact performance; therefore, test results are not presented here. All controlled tests are conducted at TTC using a chock system for automobile restraint. A TTX bi-level car loaded with two sedans and six pickup trucks is being used to test each suspension.

Test results: High speed stability

The high speed stability test is conducted on a smooth tangent track 5,000 feet long. The criterion for success is a standard deviation autorack deck lateral acceleration of no more than 0. 13 as tested at constant speed intervals from 40 to 70 mph. As shown in Figure 3, the premium suspension met the criterion while the base line three-piece truck did not. This result reflects the emphasis on high speed stability expressed by the automobile industry in past years.

Figure 4 is a time history of the autorack deck lateral acceleration and the lateral acceleration for the pickup vehicle during premium suspension tests at 70 mph. This can be compared to the unacceptable accelerations measured during the 60 mph tests with a three-piece truck shown in Figure 5. Note that the pickup and rack accelerations are similar in amplitude during each test. Results for the sedan were similar.

Test results: Pitch and bounce

The pitch and bounce tests are intended to exercise the vertical suspension. A specially constructed track with 10 vertical bumps on each rail (in phase) is used to excite the rail vehicle. Test speeds were between 40 to 70 mph. The criterion is that maximum vertical deck acceleration must be no more than 0.5 g. Results are shown only for the premium suspension.

Figure 6 shows the maximum and minimum acceleration for each speed tested. Criterion is exceeded at speeds above 55 mph. This result could be expected as this premium design does not have an improved vertical suspension. As noted earlier, automobile manufacturers have expressed concern over the vertical ride performance of this premium design.

Figure 7 shows the response of the pickup and sedan to the railcar deck accelerations. Although the recommended practice does not have a criterion for automobile acceleration, it is interesting to note that the automobile acceleration is relatively independent of the railcar deck acceleration. The sedan had much less response to the deck input than the pickup truck. This points out the need to consider the automobile suspension when evaluating suspensions for the railcar when the wheel chock method of restraint is employed.