Fast stiffness modulation of multichamber air spring suspensions for automotive applications
The doctoral research deals with the modelling and control of multichamber air springs, that are an advanced type of variable-stiffness suspension springs for ground vehicles. Indeed, the multichamber architecture is constituted by a main elastic pneumatic chamber connected to a series of (possibly dislocated) auxiliary air supplies by means of electronically controllable valves. In this way, switching the state of the valves allows one to change the total amount of air volume subject to excitation during the ride, ultimately leading to a variation of the spring equivalent stiffness ratio. For this reason, multichamber springs represent a cost effective, safe and low energy demanding solution capable of stiffness regulation, thus motivating the main car manufacturers for the industrialization of these systems over the last decade. This work aims at providing a comprehensive overview of their functioning highlighting their potentialities in enhancing both the comfort and handling performance, by addressing the open issues still present in the scientific literature up to this day and by answering the basic industrial needs. Firstly, a novel mathematical model is developed, which accurately describes the spring behaviour during fast switching; secondly, stiffness modulation strategies are proposed. These strategies have simple, effective and interpretable formulations, are real-time implementable, and require a limited number of sensors. When available, their effectiveness is also proven experimentally. Overall, the control performance surpasses the spring passivity constraint and is able to guarantee optimality and sub-optimality over a wide series of experiments, by suitably exploiting the multichamber peculiar features arising at valve switching.
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