Research and Development 5 Mar 01, page 1 Dr. W. Riley Garrott National Highway Traffic Safety Administration Vehicle Research and Test Center April 12, 2001 Recent NHTSA Dynamic Rollover Testing Experience

Research and Development 5 Mar 01, page 2 Presentation Overview Summary of Recent Testing Test Maneuvers Our Test Facilities Repeatability Outstanding Issues

Research and Development 5 Mar 01, page 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

Research and Development 5 Mar 01, page 4 Dynamic Rollover Testing Video AVI Not Included

Research and Development 5 Mar 01, page 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

Research and Development 5 Mar 01, page 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

Research and Development 5 Mar 01, page 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

Research and Development 5 Mar 01, page 8 TRC’s Vehicle Dynamics Area

Research and Development 5 Mar 01, page 9 Programmable Steering Controller

Research and Development 5 Mar 01, page 10 Rollover Instrumentation Suite

Research and Development 5 Mar 01, page 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

Research and Development 5 Mar 01, page 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%

Research and Development 5 Mar 01, page 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

Research and Development 5 Mar 01, page 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

Research and Development 5 Mar 01, page 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