Detroit—"Four-wheel steering is changing full-size pick-up trucks forever," claims Scott Sherman, a design engineer at GMC. He is one of several engineers from GMC who worked with Delphi Automotive (Saginaw, MI) designing and developing QuadraSteer for use in the 2002 Sierra Denali—the first GMC vehicle to feature the four-wheel steering system.
Sherman points out that other automotive manufacturers have tried four-wheel steering systems on compact cars. But he and Delphi Product Engineer Chad Severson believe that the improved handling and shorter turning radius that four-wheel steering provides are lost on compact cars. "Trucks are really the right application for this technology," says Severson.
QuadraSteer reduced the turning radius of a full-sized truck from 45 ft to less than 34 ft.—comparable to a Honda Civic Coupe.
When QuadraSteer is in its positive phase at high speeds, the rear wheels turn in the same direction as the front wheels. Turning the rear wheels reduces the degree of vehicle rotational motion required for the maneuver. And when pulling a trailer, the articulation angle between the wheels decreases, reducing the lateral forces applied to the rear of the vehicle. Four-wheel steering also reduces trailer sway and increases stability, especially during wind gusts, passing semis, and other tough road conditions.
In its negative phase—at low speeds—the rear wheels turn in the opposite direction of the front wheels. Here, a trailer on the back of the full-size pick-up truck more closely follows the vehicle's path, making the maneuvering of the trailer simpler for backing into tight spots.
The 2002 SIerra Denali is the first GMC vehicle to feature QuadraSteer four-wheel steering system.
Delphi's QuadraSteer system is configurable to a variety of suspension designs. The system is composed of a steerable, solid hypoid rear axle, front-wheel position sensor, electric motor driven actuator, and a control unit. The position sensors on the front wheels send information to the control unit and, depending upon the speeds, determine the best angle of steering. An automatic safety system returns the vehicle to two-wheel steering if the four-wheel driving system is damaged or if the vehicle loses power.
Sherman says the only trade-off with a four-wheel steering system is more weight on the back wheels, which isn't necessarily a bad thing on icy roads. Severson adds that the applications for the QudraSteer system may include other large vehicles such as trucks and buses.
For more information about four-wheel steering systems from Delphi Automotive: Enter 536