EAST LIBERTY, OH – A robot may be in the driver’s seat when the National Highway Traffic Safety Admin. performs its new dynamic rollover test, butMotor Corp.’s fingerprints are all over the steering wheel.
Since 2000, when Congress mandated the development of a vehicle rating system based on a methodology that simulates real-world rollover risk, NHTSA considered several test maneuvers. They included a closed-loop, double lane change procedure put forward byMotor Co.
Thenoffered up its unique “fishhook” maneuver and there was speculation as recently as last spring that it would be adopted in combination with another dynamic test.
But Jeffrey Runge, NHTSA administrator, reveals that only the fishhook will be used because it best simulates real-world conditions and effectively pushes a vehicle’s performance limits.
“We’re glad they considered it,” a Toyota spokeswoman says, adding the auto maker looks forward to comparing test results with real-world performance data.
As expected, the static stability factor – a mathematical formula that uses vehicle dimensions to predict rollover propensity – remains part of NHTSA’s vehicle rating program. Also held over is the current “star system,” designed to assign an easily understood value to test data. (See related story: SSF May be Part of New Rollover Ratings)
The fishhook employed by NHTSA, however, is not precisely like the one proffered by Toyota. “We’ve refined it,” says Michael Monk, manager of NHTSA’s laboratory here.
When NHTSA begins testing ’04 vehicles, they will be subjected to a pair of steering inputs – 270 degrees to the left, followed by 540 degrees to the right. Both will be executed within 1.5 seconds by a robotic mechanism affixed to the steering wheel.
Toyota used test drivers, whom NHTSA will replace to improve repeatability. Drivers still will be present in the vehicles but only to align the vehicle with the test area.
Once the vehicle is on course, the driver presses a button and a computer assumes control of steering and throttle. When predetermined speeds are reached, the computer releases the throttle and steering inputs are made automatically.
The fishhook is performed at 35 mph (56 km/h), 40 mph (60 km/h), 45 mph (72 km/h), 47.5 mph (76 km/h) and finally, 50 mph (80 km/h).
If, however, sensors detect simultaneous lift by two wheels that meets or exceeds 2 ins. (5.1 cm), testing for that vehicle is discontinued.
As NHTSA was developing its new test, as required by the Transportation Recall Enhancement Accountability and Documentation (TREAD) Act, auto makers and suppliers fretted over details. They wondered about tire wear, test surface continuity and climatic conditions.
Tire condition is addressed by using new product of the same variety found on test vehicles as original equipment. And before each vehicle is tested, its tires go through a “warm-up” that consists of six circles – three in each direction – and a set number of maneuvers involving sinusoidal steering inputs.
NHTSA says its test center here has adequate space to ensure test surfaces are uniform, while the only requirement for outside temperature is that it be above freezing, says W. Riley Garrott, chief of NHTSA’s vehicle stability and control division.
“Temperature is not that big of a factor,” Garrott tells Ward's.
Weight is added to simulate a load equivalent to five occupants. Unlike early tests, no weight is added to a test vehicle’s roof. This was done to exaggerate any tendency toward rollover that a vehicle might have.
To ensure the test driver’s safety, outriggers are used. Depending on vehicle size, NHTSA will use one of three sets of titanium outriggers weighing 58, 68 and 78 lbs. (26, 31 and 35 kg).
Their precise effect on test results is not known, Garrott says, but it’s believed to be negligible. “We don’t test without them for the safety of the driver,” he says.