research and development 5 mar 01, page 1

Research and Development

5 Mar 01, page 1

Dr. W. Riley GarrottNational Highway Traffic Safety Administration

Vehicle Research and Test CenterApril 12, 2001

Recent NHTSA Dynamic Recent NHTSA Dynamic Rollover Testing ExperienceRollover Testing Experience


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Presentation Overview

• Summary of Recent Testing• Test Maneuvers• Our Test Facilities• Repeatability• Outstanding Issues


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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


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Dynamic Rollover Testing Video

AVI Not Included


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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


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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


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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


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TRC’s Vehicle Dynamics Area


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Programmable Steering Controller


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Rollover Instrumentation Suite


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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


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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%


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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


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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


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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

research and development 5 mar 01, page 1

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