Automotive Spin Control: Working to Build a Safer Vehicle

A sharp yank on the steering wheel at high speed is all too often the triggering event for a serious accident. Once control of a vehicle is lost at high speed, most drivers confront disaster, unable to regain control.

Although driver error is at the root of most single-vehicle skids, auto makers have been working for a decade to develop advanced technology systems to help prevent loss of control.

Imagine traveling down a highway at 50 to 70 miles an hour when you suddenly spot a road hazard--an animal, a stalled car, a pedestrian or some type of debris--that requires a quick response.

Human instinct is to jerk the steering wheel quickly, causing the car to veer sharply.

All too often, the steering input is far greater than required to avoid the obstacle and too much for the car’s suspension system to handle, according to Bob Lange, executive director for safety integration at General Motors.

As the vehicle’s rear wheels begin to skid outward in a fishtail, the driver instinctively cranks the steering wheel in the opposite direction in an attempt to compensate.

The sprung mass of the vehicle begins a harmonic rocking that seals the deal, eliminating any chance of regaining control.

Most vehicles will not flip over merely because of a spin-out.

But sport-utility vehicles, with their high center of gravity, are far more vulnerable to rollover. However, even SUVs do not always tip just because of a sideways skid.

The majority of rollovers are caused when the sliding vehicle strikes a curb or a soft shoulder.

Better emergency-maneuver training for drivers would seem to be in order.

But few, if any, states require drivers to improve specific skills, as long as they can pass a rudimentary written exam and driving test. In some states, motorists are never retested after obtaining that initial license.

And so the responsibility has fallen upon the auto makers to try to design and build cars that are more resistant to loss of control.

Electronic stability control has become the key technology in efforts to help prevent spin-outs, but suspension manufacturers are also studying mechanical systems that could help vehicles remain stable in severe maneuvers.

General Motors, which has included electronic stability control systems on some of its cars since the mid-1990s, has one of the largest and most sophisticated research programs in the industry.

It currently offers such systems on 10 of its models, representing about half of its passenger car production. So far, the systems are not available on GM trucks or sport-utility vehicles.

Some other manufacturers, including Toyota and BMW, also offer these systems.

Toyota, for example, offers it as either an option or as standard equipment on its 4Runner, Land Cruiser and Avalon models.

Ford Motor, meantime, says it will offer skid control on its new 2002 Explorer and Mercury Mountaineer SUVs beginning later this year.

The GM system, like others, uses a suite of computerized sensors to detect the onset of a skid and instantly compensate for it before the driver has a chance to overreact, Lange said.

As a vehicle’s rear-end begins to slide, a yaw sensor--which measures lateral forces that deviate from the line of travel--detects the skid and uses sophisticated electronics to apply the brakes at various combinations of wheels.

The system also has the ability to reduce engine power in certain situations, such as a skid on a curve.

The whole sequence of events occurs in thousandths of a second.

If the yaw can be held to a minimum, the driver is not tempted to overcorrect for the skid, Lange said. Generally, a yaw that pulls the rear-end more than 30 degrees off the line of travel can never be corrected.

Lange could not quantify how much more of a safety margin GM’s system may provide, but he termed the improvement “dramatic.”

A completely different, mechanical, approach to stability control is under development at Tenneco Corp., manufacturer of Monroe brand shock absorbers and struts.

As a driver negotiates bumps and turns, the weight of a vehicle shifts between the wheels.

In a high-speed turn, for example, centrifugal force throws more of the weight to the outboard wheels.

The Tenneco system is designed to compensate for that by shifting some of the weight back to the inboard wheels, according to Dave Boucher, director of advance suspension technology at Tenneco.

The concept is to interconnect the suspension of all four wheels, allowing them to operate independently in some instances and as a unified system in other instances--all without electronic control.

“When you jerk the steering wheel, you want the wheels to stay on the ground,” Boucher said. “This interconnection allows us to maintain equal loading on the ground.”

The company says it has a deal with a major manufacturer, but it is not yet known which vehicles will someday have the new system.

The system design would depend on the vehicle, but it can use hydraulic actuators, hydraulic lines, check valves and other parts that are typical of hydraulic systems. The design does not employ on any computer controls, but rather depends on the use of hydraulic forces created at one wheel to compensate at another.

Although stability control is still a fairly novel idea, it will someday become a routine part of every vehicle.

“As people become more aware of it,” Lange said, “the market will grow substantially, possibly large enough to require it as standard” equipment on all vehicles.

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Ralph Vartabedian cannot answer mail personally but responds

in this column to automotive questions of general interest. Please do not telephone. Write to Your Wheels, Business Section, Los Angeles Times, 202 W. 1st St.,

Los Angeles, CA 90012. E-mail: ralph.vartabedian@latimes.com.