In the general context of vehicles' fuel consumption and emissions reduction, the minimization of the aerodynamic drag can offer not negligible benefits regarding the environmental issues. The adjustment of the vehicle height is one of the possible ways to provide a reduction of the resistances to vehicle motion, in addition to consequent aspects regarding the increased versatility of the vehicle. The aim of this paper is to present in a systematic way to the state of the art of height adjustment systems for passenger vehicles, summarizing the main modes of operations, working principles and architectures. Particular attention is then given to electromechanical systems, which represent the next trends for future vehicles due to their high reliability and relatively low costs. A design methodology for electromechanical height adjustment systems with the purpose of optimizing their performance is presented. Such procedure is able to reach the most efficient working point even in presence of constraints of different nature. Prototypes have been designed, produced and tested to demonstrate the potentialities of electromechanical height adjustment systems. Furthermore, potential benefits and drawbacks of using such systems are highlighted.

Vehicle driveability describes the complex interactions between the driver and the vehicle, mainly related to longitudinal vibrations. Today, a relevant part of the driveability process optimization is realized by means of track tests, which require a considerable effort due to the number of parameters (such as stiffness and damping components) affecting this behavior. The drawback of this approach is that it is carried on at a stage when a design iteration becomes very expensive in terms of time and cost. The objective of this work is to propose a light and accurate tool to represent the relevant quantities involved in the driveability analysis, and to understand which are the main vehicle parameters that influence the torsional vibrations transmitted to the driver. Particular attention is devoted to the role of the tire, the engine mount, the dual mass flywheel and their possible interactions. The presented non linear dynamic model has been validated in time and frequency domain and, through linearization of its non linear components, allows to exploit modal and energy analysis. Objective indexes regarding the driving comfort are additionally considered in order to evaluate possible driveability improvements related to the sensitivity of powertrain parameters.

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The term driveability describes the driver's complex subjective perception of the interactions with the vehicle. One of them is associated to longitudinal acceleration aspects. A relevant contribution to the driveability optimization process is, nowadays, realized by means of track tests during which a considerable amount of driveline parameters are tuned in order to obtain a good compromise of longitudinal acceleration response. Unfortunately, this process is carried out at a development stage when a design iteration becomes too expensive. In addition, the actual trend of downsizing and supercharging the engines leads to higher vibrations that are transmitted to the vehicle. A large effort is therefore dedicated to develop, test and implement ignition strategies addressed to minimize the torque irregularities. Such strategies could penalize the engine maximum performance, efficiency and emissions. The introduction of the dual mass flywheel is beneficial to this end. Nevertheless, its role on the vehicle driveability, as well as that of other driveline components, is not yet so clear. The aim of the present work is to establish which are the main driveline components affecting the filtering behavior of the transmission and how their parameters can be tuned in order to improve the vehicle ability to respond to driver's different demands without negative impact on his comfort. A complete nonlinear coupled torsional and longitudinal vehicle dynamic model is proposed to this end. The model is validated both in time and frequency domain and allows linearization of its nonlinear components.

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