Auto Service World
News   February 12, 2002   by Auto Service World

Four-wheel Steering Slated for GM Full-Sized Pickups

Delphi Automotive Systems has announced that its four-wheel steering system, which debuted on GMC Sierra Denali full size trucks this year, will be available in the 2002 calendar year on GMC Sierra and Chevy Silverado 1/2 ton, extended cab short box trucks.
The company also announced that the system, knows as QuadraSteer, will be optional on 2003 models that include the Chevrolet Silverado and GMC Sierra 1500HD short box crew cabs and Chevrolet Suburban and GMC Yukon XL 3/4 ton full-size sport utility vehicles.
“We are very pleased to see QuadraSteer available across more vehicle platforms at General Motors,” stated Paul J. Tosch, president of Delphi Saginaw Steering Systems and vice president of Delphi Automotive Systems. “Full size SUVs are the next logical step for vehicles which will benefit from this revolutionary system. QuadraSteer will enhance their consumer value through the added maneuverability and stability as seen now on the Sierra Denali.”
GMC is also featuring QuadraSteer by Delphi on their new concept truck, Terra4, which debuted at the Chicago Auto Show last week. The Terra4 is a four-door, four-wheel drive, four-wheel steer utility truck with four doors and four ways to access the cargo bay.
It is intended to meet the needs of a truck market that has shifted away from traditional utility, work use to personal use.
QuadraSteer combines conventional front-wheel steering with an electrically powered rear-wheel steering system. The system has four main components — a front-wheel position sensor, steerable solid hypoid rear axle, electric motor-driven actuator, and a control unit.
Handwheel position and vehicle speed sensors continuously report data to the control unit, which in turn determine the appropriate angle of the rear wheels. Algorithms are then used to determine the correct phase of operation. The system operates in three principal phases: negative, neutral, and positive. At lower speeds, the rear wheels turn in the opposite direction of the front wheels. This is the negative phase. At moderate speeds, the rear wheels remain straight or neutral. At higher speeds, the rear wheels are in the positive phase, turning in the same direction as the front wheels.
QuadraSteer will give added control to full-size vehicle drivers that trailer. During low-speed, negative-phase towing maneuvers, the trailer follows the true vehicle path much more closely than with two-wheel steering. This makes driving in city traffic with a trailer easier. Low-speed maneuvering such as backing into a boat launch or parking a camper is also easier with QuadraSteer. When backing a trailer, the negative phase greatly improves the trailer response to steering inputs, making it easier to place the trailer into position.
At higher speeds, trailering stability is significantly enhanced. The positive rear steering phase reduces the articulation angle between the vehicle and trailer, which reduces the lateral forces applied to the rear of the vehicle by the trailer. This, in turn, reduces the yaw velocity gain and increases yaw damping of the vehicle and the trailer system. The net result is increased trailering stability, reduced trailer sway and reduced driver corrective steering to external disturbances such as wind gusts, semi-truck passing and irregular road surfaces.
Larry Tomczak, director of engineering at Delphi’s Saginaw Steering Systems division, adds that, “QuadraSteer also enhances stability at higher speeds when there is no trailer. Steering the rear wheels in the same direction as the front wheels at higher speeds helps reduce the vehicle yaw, or rotational motion, required to accomplish a maneuver, thus helping to stabilize the vehicle response during passing, lane change or evasive maneuvers even under adverse road conditions.”

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