In road vehicles, wheel locking can be prevented by means of closed-loop anti-lock braking systems (ABS). Automatic braking is extensively used also for electronic stability control (ESC) systems. In braking control systems, two output variables are usually considered for regulation purposes: wheel deceleration and wheel longitudinal slip. Wheel deceleration is the controlled output traditionally used in ABS, since it can be easily measured with a simple wheel encoder; however, the dynamics of a classical regulation loop on the wheel deceleration critically depend on the road conditions. A regulation loop on the wheel longitudinal slip is simpler and dynamically robust; moreover, slip control is perfectly suited for both ABS and ESC applications. However, the wheel-slip measurement is critical, since it requires the estimation of the longitudinal speed of the vehicle body, which cannot be directly measured. Noise sensitivity of slip control hence is a critical issue, especially at low speed. In this work a new control strategy called mixed slip-deceleration (MSD) control is proposed: the basic idea is that the regulated variable is a convex combination of wheel deceleration and longitudinal slip. This strategy turns out to be very powerful and flexible: it inherits all the attractive dynamical features of slip control, while providing a much lower sensitivity to slip-measurement noise.

Several state of the art papers and even books on brake vibration and/or noise have been presented in the literature. Many of them have analytically and sharply accounted for the impressive amount of research undertaken on this topic. This state of the art review focuses on the still-open questions that appear crucial from the perspective of a leading brake manufacturer. The paper deals with the phenomena of brake vibration and/or noise, the experimental and theoretical methods for studying such phenomena, and the actions that are identified to be necessary to definitely solve the addressed problem. Key topics are the modelling of friction, the modelling of the dynamics of the brake as a non-linear system subjected to deterministic or random (parametric) excitation, the proper modelling of the contact between the disc and the pad, and the experimental validation of the mathematical models.

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Abstract. In road vehicles, wheel locking can be prevented by means of closedloop Anti-lock Braking Systems (ABS). Two output measured variables are usually considered for regulation: wheel-deceleration and wheel longitudinal slip. The traditional controlled variable used in ABS is the wheel deceleration, since it can be easily measured with a simple wheel encoder; however, it can be dynamically critical if the road-surface rapidly changes. On the other hand, the regulation of the longitudinal slip is much robust from the dynamical point of view, but the slip measurement is critical, since it requires the estimation of the longitudinal vehicle speed. In this work a control strategy is proposed, where the regulated variable is a combination of wheel deceleration and longitudinal slip.

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