ON THE REFORMULATION OF THE ABS LOGIC BY SENSING FORCES AND MOMENTS AT THE WHEELS Juan C. Botero, Massimiliano Gobbi, Giampiero Mastinu *,1 Nicola Di Piazza, Rosario Martorana ** * Politecnico di Milano (Technical University) Department of Mechanical Engineering via La Masa, 34 - 20156 Milano, Italy ** STMicroelectronics Advanced System Technology (AST) Stradale Primosole 50 - 95121 Catania, Italy Abstract: This paper develops a new strategy for the control of road vehicles dynamics based on the measurements of the forces acting on the tyres. An Anti– Lock Braking System (ABS) has been developed by using Sliding Mode Control. A patented system is used to measure the forces and moments acting on each tyre. Simulation results indicate that the implementation of the proposed algorithm is not only capable of reducing the stopping distance in a hard–braking maneuver by 10 % in average, but also of improving steerability and controllability of the vehicle in different driving conditions. Copyright c 2007 IFAC Keywords: Antilock braking systems, Vehicle dynamics, Sliding mode control. 1. INTRODUCTION In the following paper, a new Anti–lock Braking System control strategy based on tyre force mea- surements is presented. For a complete overview of current commercial and State–of–the–art systems for the control of the horizontal motion of road vehicles, refer to (van Zanten, 2006). Although the idea to keep the wheels from locking in order to improve steerability dates back to the beginning of the 20th century, the first modern electroni- cally controlled Anti–Lock Braking System was not installed until 1978. First research attempts on feedback control of the stability and steerabil- ity of road vehicles by controlling the individual wheel slips were given in 1973, before ABS en- tered the automotive market(van Zanten, 2006). A complete review on modern automotive brake systems is given in (BOSCH, 1995). One of the 1 Corresponding author: mastinu@mecc.polimi.it pioneers in the development of these systems was Anton Th. van Zanten, whose ideas have been transmitted in many books and specialized arti- cles (van Zanten et al., 1998; van Zanten, 2000, 2006, and the references therein). Most of the algorithms used in Vehicle Dynamics Control are based on on–line measurements of the state of the vehicle. Some measurements are simply and di- rectly taken, such as the wheels angular velocities. Some other measurements are more complicated to obtain, e.g. body slip angle of the vehicle or, in particular, the forces at the tyres. As a conse- quence, many algorithms make use of parameter estimation techniques to estimate different needed variables ( S. E. Shladover et al. 1991). Extended Kalman Filters (EKF) is a popular and widely used on–line parameter estimation technique. In the automotive environment Extended Kalman Filters are commonly used to estimate tyre forces (Ray, 1995; Wilkin et al., 2005, 2006). Even in