Dr. W. Riley Garrott National Highway Traffic Safety Administration

1. Recent NHTSA Dynamic Rollover Testing Experience Dr. W. Riley Garrott National Highway Traffic Safety Administration Vehicle Research and Test Center April 12, 2001

2. Presentation Overview • Summary of Recent Testing • Test Maneuvers • Our Test Facilities • Repeatability • Outstanding Issues

3. Summary of Recent Testing • NHTSA has been performing dynamic rollover testing steadily since fall of 1996 • Isuzu Trooper investigation in 1996 • Phase I-A research in 1997 • Phase I-B research in 1997 – 98 • Phase II research in 1998 • Phase III research in 1999 – 2000 • Ford Explorer investigation in 2000 • Phase IV research in 2001

4. Dynamic Rollover Testing Video AVI Not Included

5. Test Maneuvers • Two broad categories • Open-loop. Handwheel steering angle is specified function of time • J-Turn • J-Turn with Pulse Braking • Fishhooks (reverse steer) • Resonant Steer • Single Sine • Each of above has many variations

6. Test Maneuvers • Closed-loop. Handwheel steering angle varies according to actions of vehicle • Driver closes feedback loop • Double Lane Change • Off-Road Recovery simulation • Instrumentation closes feedback loop • Fishhook with Roll Rate Feedback

7. Our Test Facilities • VRTC located on the grounds of the Transportation Research Center, Inc. • Major automotive proving grounds • TRC’s Vehicle Dynamics Area – the large, flat paved area needed for dynamic rollover testing • Programmable steering controller • Rollover instrumentation suite

8. TRC’s Vehicle Dynamics Area

9. Programmable Steering Controller

10. Rollover Instrumentation Suite

11. Repeatability • During dynamic rollover testing, vehicles become highly non-linear • Small changes in inputs, test conditions can lead to large changes in test outcomes • Testing in early-70’s found up to 40% run-to-run variability

12. Repeatability • Have had good repeatability in our testing • Major improvement over 70’s • Less tire wear with radial tires plus better equipment • Open-loop maneuver repeatability • Peak lateral accelerations – 0.05 g • Peak roll angles – 0.5 degrees • Minimum speed for two-wheel lifts to occur – 2 mph • Closed-loop double lane change repeatability • Maximum traversal speed – 10%

13. Issues • Maneuver(s) to use for rollover ratings • Ensuring that cannot get good rollover rating by degrading vehicle handling • By putting tires with poor traction on a vehicle, can prevent two-wheel lifts in these maneuvers • Safety may be degraded because cannot turn as sharply • Use of two-wheel lifts as safety-relevant measure • Minor two-wheel lifts may not be safety issue • Requiring major two-wheel lifts may cause test driver safety problems

14. Issues • Longer-term repeatability • Effects of weather of results • Summer versus winter • Changes to the same test surface with time • Reproducibility • Effects of testing on different test surfaces

15. Issues • Outrigger effects • Must have for safety, prevention of test surface damage • How do they change a vehicles rollover propensity? • Tire wear • How much testing can be performed on a set of tires before wear effects become significant • Tire debeading • What to do if tires debead while performing rollover rating testing