Road identification for anti-lock brake systems equipped with only wheel speed sensors

Anti-Lock brake systems (ABS) are now widely used on motor vehicles. To reduce product cost and to use currently available technologies, standard ABS uses only wheel speed sensors to detect wheel angular velocities, which is not enough to directly obtain wheel slip ratios needed by the contrd unit, but can be used to calculate reference slip ratios with measured wheel angular velocities and the estimated vehicle speed. Therefore, the road friction coefficient, which determines the vehicle deceleration during severe braking, is an important parameter in estimating vehicle speed. This paper analyzes wheel acceleration responses in simulations of severe braking on different road surfaces and selects a pair of specific points to identify the wheel acceleration curve for each operating condition, such as road surface, pedal-braking torque and wheel vertical load. It was found that the curve using the selected points for each road surface clearly differs from that of the other road surfaces. Therefore, different road surfaces can be distinguished with these selected points which represent their corresponding road surfaces. The analysis assumes that only wheel speed sensors are available as hardware and that the road cohesion condition can be determined in the initial part of the severe braking process.