Hanover, Germany —Critical information about road conditions and handling performance can be obtained by monitoring tire deformation. That is the premise of a new Sidewall Torsion Sensor (SWT) designed to give acceleration, deceleration, and cornering data to a vehicle's Electronic Stability Program (ESP).
To integrate the SWT sensor, Continental AG adds a magnetic powder to the tire compound during the production process. Tires are then magnetized with north and south pole domains in the side wall circumference. Two inductive sensors per wheel attach to the vehicle chassis, one above the other.
Two magnetic sensors attached to the chassis detect
magnetized powder mixed with the tire's side-wall
As the tire rotates, sensor signals remain in phase if there are no
longitudinal forces acting on the wheel. During a maneuver, however, the tire
distorts with the outer part moving relative to the inner part. This results in
a timing offset between sensor signals. A computer determines the longitudinal
force from the time difference.
Comparing signal amplitudes, rather than timing, monitors lateral forces on the tire as the car corners. In this case, the outer part of the tire develops a lateral offset compared to the inner part, resulting in different distances to their respective sensors. Different magnetic field strengths received at the sensors produce the discrepancy in signal amplitudes.
"SWT makes it possible for the ABS control device to adjust the slip curves much more exactly to optimize high braking deceleration while the driving condition is still stable," claims Heinrich Huinink, vice president of research and process technology at Continental.