Abstract
Anti-lock brake systems (ABS) are now widely accepted and used on more and more motor vehicles. With the consideration of low product cost and technologies currently available, standard ABS has only wheel speed sensors to detect wheel angular velocities, not enough to directly obtain wheel slip ratios needed by control unit, but to calculate reference slip ratios with measured wheel angular velocities and estimated vehicle speed. Therefore, the road friction coefficient, which dominates vehicle deceleration during severe braking, is an important parameter in estimating vehicle speed. This paper analyzed wheel acceleration responses in simulations of severe braking on different road surfaces, and selected a pair of specific points to mark the wheel acceleration curve under each certain operating condition, such as road surface, pedal-braking torque and wheel vertical load. It was found that the curve of selected points of one road surface is clearly different from that of the other road surfaces. That means different road surfaces can be distinguished with those selected points, which represent their corresponding road surfaces. Only wheel speed sensors are assumed available as hardware, and the road cohesion condition can be determined in the initial process of severe braking.