This study investigates amplified hydraulic braking systems employed in high-performance motorsport applications, utilizing wedge mechanisms for self-energization. An analytical expression for the gain coefficient is derived from a simplified equilibrium analysis of the wedge-shaped pad, capturing the nonlinear dependency on both wedge angle and effective mean disc-pad friction. A previously validated coupled thermoelastic model for carbon-carbon (C/C) braking systems—developed in Dymola and Modelica using the finite volume method (FVM) and an analytical local friction formulation—is here adapted to wedge-amplified braking systems, with the aim of providing performance assessment during the design phase of new calipers at reduced computational cost compared to coupled thermoelastic finite element method (FEM) models. Several caliper configurations featuring different wedge angles are tested experimentally on a dynamometer. A reduction in the effective friction coefficient at high mean effective contact pressure—induced by pronounced wedge angles and reduced pad areas—is observed. To validate the thermoelastic model, simulated braking torque and disc surface temperature are compared against bench data. The model shows satisfactory predictive capability under various operating conditions and test cycles, with mean error indices on peak torque prediction below 5% for the majority of the simulated cases. Finally, the validated model is used to virtually assess the performance of a new caliper prototype prior to its manufacturing and testing.

The paper aims to explain in the simplest possible way how tyres influence, to the greatest extent, the dynamic behaviour of cars, i.e. vehicle handling, during power-on or power-off. Starting from the ISO 4138 steering pad test, controlled power-on and power-off manoeuvres are introduced to reproduce typical manoeuvres relevant for active safety. Handling diagrams are used to make clear how tyres determine the oversteer and understeer character of a car. A simple two degrees-of-freedom analytical vehicle model and a complex high-fidelity fourteen degrees-of-freedom model have been used. Driver-in-the-Loop simulations were performed at a dynamic driving simulator. The study considers three representative driveline configurations, namely front-wheel drive (FWD), rear-wheel drive (RWD), and all-wheel drive (AWD). A key outcome of the study is that the fundamental mechanisms governing understeer and oversteer behaviour can be effectively captured using a simple two degrees-of-freedom model combined with appropriate tyre characteristics. The results show that the handling diagrams are a proper tool to describe handling manoeuvres during power-on or power-off. Variations in understeer and oversteer behaviour induced by power modulation can be interpreted as a direct consequence of tyre characteristics. The findings of this work highlight the pivotal role of the tyre in vehicle dynamics and active safety.

Noise, Vibration and Harshness (NVH) is a key aspect in the design of electric motors for electrified vehicles, as mechanical vibrations induced by electromagnetic forces are the main source of noise. In this paper, topology optimization is employed to design the rotor of a 6-pole/36-slots Permanent Magnet Synchronous Motor (PMSM) for automotive applications. Starting from a reference motor, the rotor is optimized considering both electromagnetic and structural requirements in the software Altair Flux. The target is minimizing the 6th and 12th torque harmonics to reduce both torque ripple and noise emission across the operating speed range. Constraints are imposed on the minimum delivered torque and on the radial deformation to ensure the structural safety of the rotor. A SIMP-based interpolation scheme is used to penalize the magnetic reluctivity. The NVH performance is assessed through a simplified analytical model, where stator, windings, and housing are represented as an equivalent curved beam. Starting from the excitation produced by the electromagnetic forces, closed-form solutions are used to estimate natural frequencies, vibration amplitudes, and radiated sound pressure of the beam. The optimized design is compared with the reference motor in terms of torque performance, structural response, and acoustic emission.

The aim of the article is to evaluate the effect of the cooling system on the NVH behavior of traction permanent magnets synchronous motors (PMSMs). An effective numerical method is proposed for modeling the fluid–structure interaction in the cooling system of PMSMs. A simplified physical prototype of a cooling jacket of a PMSM is realized by welding two concentric tubes with an internal cavity filled by coolant. A finite element model of the structure is realized. The coolant is modeled as an acoustic domain to account for the fluid–structure interaction in the cavity and a coupled acoustic–structural dynamic problem is solved. The model is validated by experimental modal tests conducted on the prototype of the cooling jacket both with and without the presence of coolant. The validated model is employed to quantify the effect of the cooling system on a real PMSM. The structure of a 10-poles, 12-slots electric machine is modeled by means of finite element method. The model includes the validated cooling jacket and the internal stator lamination and windings. Numerical vibroacoustic analyses have been performed at different operating conditions, either with or without modeling the coolant with the aim of quantifying its effect on the sound emission of the machine. Acoustic emission is generally increased when fluid coolant is present. For a PMSM, localized sound emission peaks appeared in the low-frequency range, up to 2000 Hz. A maximum increase of 44 dB was observed.

The article investigates how to detect as quickly as possible whether the driver will lose control of a vehicle, after a disturbance has occurred. Typical disturbances refer to wind gusts, obstacle avoidance, a sudden steer, traversing a pothole, a kick by another vehicle, and so on. The driver may be either human or non-human. Focus will be devoted to human drivers, but the extension to automated or autonomous cars is straightforward. Since the dynamic behavior of vehicle and driver is described by a saddle-type limit cycle, a proper theory is developed to use the limit cycle as a reference trajectory to forecast the loss of control. The Floquet theory has been used to compute a scalar index to forecast stable or unstable motion. The scalar index, named degree of stability (DoS), is computed very early, in the best case, in a few milliseconds after the disturbance has ended. Investigations have been performed at a dynamic driving simulator. A 14 DoF vehicle model, virtually driven by a real human driver, was employed. A number of evasive maneuvers have been examined, both for understeer and oversteer vehicles. The early detection of the loss of control is possible. The sensing of the loss of control could be enhanced with respect to a classical ESP, although a more in-depth investigation is needed. Some issues referring to the robustness of the computation of the DoS are still to be investigated. Nonetheless the DoS seems already applicable for motorsport vehicle and drivers.

The paper is devoted to the measurement of aircraft tyres' characteristics. Namely the low and high frequency characterisation of aircraft tyres is performed. A new testing system for the indoor characterisation of aircraft tyres is presented. Two test rigs, one for the low frequency and one for high frequency tests, have been designed and realised. Measured data are processed according with the standard PAC2002, together with a short-wavelength intermediate frequency (SWIFT) model and a 3D tandem cam filter for high frequency dynamic and obstacle enveloping, i.e., the tyre model developed for automotive tyre has been employed to describe the behaviour of aircraft tyres. The results show that the low frequency behaviour of aircraft tyres can be accurately reproduced by PAC2002. Obstacle enveloping and high frequency characteristics are captured by the considered model with a sufficient degree of accuracy for engineering applications. Should dedicated noise-vibration harshness simulations be performed, this model, developed for automotive applications, should be revised for aircraft tyres.

The aim of this paper is to introduce a novel Anti-lock Brake System (ABS) based on Sliding Mode Control (SMC). The control makes use of forces and moments provided by a novel sensorized hub carrier with sensorized brake caliper. SMC ABS performance has been assessed by comparing it with a rule-based ABS logic. The comparison is performed via simulation, using a complex 14-dof vehicle model that is intended to represent a high-performance sports car. The SMC ABS relies on the vertical force, lateral force, longitudinal force at the tire and brake torque. Such measurements are used to estimate the friction coefficient between the tire and the road surface. A full brake maneuver has been simulated in multiple scenarios either with dry tarmac, with wet tarmac or $\mu $ -split. The results indicate that the novel ABS allows a reduction in braking distance compared to the traditional ABS, particularly on low-friction roads. This improvement is attributed to the system’s ability to rapidly identify the road’s friction coefficient and adjust the brake torque in order to maximize the longitudinal tire performance.

The global stability of car-and-driver is studied. The aim is to distinguish stable versus unstable trajectories as early as possible, after a disturbance has acted. First, a simple car-and-driver model is introduced to simulate the response of the system to severe perturbations, e.g. wind gusts or evasive maneuvers. Both straight and curved motions are analysed, considering an oversteering vehicle. The motion of the system is influenced by the existence of unstable limit cycles, generated from a Hopf bifurcation that occurs at relatively high vehicle forward velocity. Resorting to bifurcation theory, we demonstrate that unstable limit cycles are saddle-type cycles with an N-1 -dimensional stable manifold, being N the dimension of the system. Such stable manifold divides the phase space into two regions, delimiting the stability region of the vehicle. Initial states outside this region cause an uncontrolled motion. By exploiting the properties of the manifolds and by resorting to Floquet theory, we derive a Degree of Stability (DoS) criterion valid for motions close to the saddle limit cycle. The criterion serves as a strategy to promptly detect unstable car-and-driver motion in real time during a maneuver, also offering a quantitative indication of the severity of the instability. Two examples show that the DoS criterion can distinguish between a controlled and an uncontrolled maneuver when the corresponding trajectories are still almost equivalent.

This paper deals with an adaptive multi-objective optimisation process for the design of electric motors by means of supervised learning techniques. The process is based on a multi-objective optimisation approach which involves many objective functions (mass, rotor inertia, average total losses), constraints (geometrical feasibility, current and voltage limit, torque-speed profile, thermal constraints) and a large number of design variables (rotor, stator and winding parameters) that describe the physical properties of the motor. The design of computer experiments is based on a Low Discrepancy Sequence (LDS).The electric motor performance indices are evaluated through multiphysics simulations (electromagnetic, thermal) carried out by Motor-CAD(TM) software. Artificial Intelligence (AI) is adopted to approximate the physical model behaviour. Artificial Neural Networks (ANN) are exploited, in this way a large set of design variables combinations can be investigated with a reasonable computational effort. Since the multi-objective optimisation of electric motor is particularly complex, a special algorithm had to be developed to find Pareto-Optimal solutions. A new Adaptive Pareto Algorithm allows to reduce the computational cost and to achieve an even distribution of the optimal solutions in the Pareto optimal front. The algorithm is particularly effective when it is integrated with a global approximation model, the infill operation allows to improve the metamodel approximation. The derived electric motors show the best compromise performances among millions of possible configurations.

An electric motor exhibits structural dynamic excitation at high frequency, making it particularly prone to noise, vibration, and harshness (NVH) problems. To mitigate this effect, this article discusses a novel countermeasure technique to improve NVH performances of electric machines. A viscoelastic rubber layer is applied on the outer surface of a permanent magnet synchronous motor (PMSM) as vibration damping treatment. The goal is to assess the countermeasure effectiveness in reducing acoustic emissions at different temperatures, through a combination of numerical modeling and experimental validation. A finite element model of the structure is realized, considering a viscoelastic material model for the rubber material, with frequency-dependent loss factor and storage modulus. The numerical model is validated by means of experimental modal tests performed on a housebuilt cylindrical structure, designed to mimic the geometry of a typical cooling jacket of a PMSM for automotive applications. The structure of a 10-pole 12-slots electric motor and the validated cooling jacket are modeled using finite element method (FEM). Vibro-acoustic simulations were carried out both with and without the presence of the viscoelastic damping layer. Results demonstrate that the application of the viscoelastic layer effectively reduces acoustic emissions, achieving a reduction of 9 dB.

Evaluating noise, vibration, and harshness (NVH) performance is crucial in vehicle development. However, NVH evaluation is often subjective and challenging to achieve through numerical simulation, and typically prototypes are required. Dynamic driving simulators are emerging as a viable solution for assessing NVH performance in the early development phase before physical prototypes are available. However, most current simulators can reproduce vibrations only in a single direction or within a limited frequency range. This paper presents a comprehensive design optimization approach to enhance the dynamic response of a full-spectrum driving simulator, addressing these limitations. Specifically, in complex driving simulators, vibration crosstalk is a critical and common issue, which usually leads to an inaccurate dynamic response of the system, compromising the realism of the driving experience. Vibration crosstalk manifests as undesired vibration components in directions other than the main excitation direction due to structural coupling. To limit the system crosstalk, a flexible multibody dynamics model of the driving simulator has been developed, validated, and employed for a global sensitivity analysis. From this analysis, it turns out that the bushings located below the seat play a crucial role in the crosstalk characteristics of the system and can be effectively optimized to obtain the desired performances. Bushings’ stiffness and locations have been used as design variables in a multiobjective optimization with the aims of increasing the direct transmissibility of the actuators’ excitation and, at the same time, reducing the crosstalk contributions. A surrogate model approach is employed for reducing the computational cost of the process. The results show substantial crosstalk reduction, up to 57%. The proposed method can be effectively applied to improve the dynamic response of driving simulators allowing for their extensive use in the assessment of vehicles’ NVH performances.

The aim of the paper is to clarify the semantic and thus the difference between tyre rolling resistance and tyre rolling loss. Reference is exclusively made to longitudinal forces. The focus is on which are the actual forces and moments that cause a dissipated power during tyre rolling. The equilibrium equation for rotation of the wheel is unable to describe which are such actual forces and moments. In accordance with the existing literature, the power balance of rolling tyre is more suitable to identify the actual forces and moments causing dissipated power. We propose to refer to “rolling resistance” when the longitudinal slip is vanishing or low and to refer to “rolling loss” when the longitudinal slip is relatively high. A new index defining the rolling loss is proposed, namely the tyre rolling dissipation index (TRDI). The theoretical investigation is substantiated by an experimental activity performed via a new trailer for tyre testing. The rolling resistance torque, the external applied torque, the wheel axle height, the longitudinal force at the hub and the kinematics of the rim have been measured and combined to describe the TRDI. Results shows that tyre rolling loss increases as a braking torque is applied to the wheel and the effect of the TRDI is shown as function of longitudinal slip. A practical rule is proposed, stating that the ratio of tyre dissipated power to the total dissipated power is nearly equal to the longitudinal slip.

The research activity aims at defining specific Operational Design Domains (ODDs) representative of Italian traffic environments. The paper focuses on the human-machine interaction in Automated Driving (AD), with a focus on take-over scenarios. The study, part of the European/Italian project “Interaction of Humans with Level 4 AVs in an Italian Environment - HL4IT”, describes suitable methods to investigate the effect of the Take-Over Request (TOR) on the human driver’s psychophysiological response. The DriSMI dynamic driving simulator at Politecnico di Milano has been used to analyse three different take-over situations. Participants are required to regain control of the vehicle, after a take-over request, and to navigate through a urban, suburban and highway scenario. The psychophysiological characterization of the drivers, through psychological questionnaires and physiological measures, allows for analyzing human factors in automated vehicles interactions and for contributing to advance AD technologies. Physiological signals, including electrocardiographic (ECG) and electroencephalographic (EEG) are acquired synchronously with eye-tracking and instrumented steering wheel signals throughout the entire test. The use of dynamic driving simulation enhances the study’s efficacy, facilitating early-stage development insights crucial for the advancement of AD technologies.

The paper presents an innovative moving laboratory (MoLAS) for tire testing. The MoLAS system is mounted on a semitrailer to be pulled for outdoor tire characterization under realistic grip condition. The vertical load is controlled by means of a pneumatic spring actuator mounted on top of a moving platform guided by linear ball sliders. A double-stage suspension system allows to filter out the vertical disturbance induced by road irregularity. Two electric actuators are used to precisely control steering and camber angles. Tire forces and moments are measured by an innovative six-axis force sensor specifically designed for the purpose. The main innovation introduced by the MoLAS with respect to the state-of-art test systems relies in the possibility to test the tire both in traction and braking longitudinal slip conditions. This is achieved by an internal combustion engine and a retarder electromagnetic brake mounted on the driveline. A complete tire characterization has been performed by placing the MoLAS system on the RuotaVia drum of the LaST laboratory at Politecnico di Milano. The main results are presented in the paper.

Accurate accident reconstruction requires the knowledge of the mass properties of vehicles, namely the centre of gravity location, the mass and the inertia tensor. Such data are seldom available, especially in case of newly produced electric vehicles. In this paper, vehicle inertia measurements, performed at Politecnico di Milano, refer to a number of electric vehicles. In addition to the “simple” measurement of vehicle inertia, measured mass properties are analysed to derive the proper empirical formulae for the estimation of the centre of gravity height and the moments of inertia. Both internal combustion and electric vehicles are considered. Data show a significant difference in the mass properties of the two types of vehicles. The proposed formulae can be effectively employed to quickly obtain a reasonable estimation of the mass properties of any vehicle. The results show that electric vehicles are characterised by higher values of mass with respect to internal combustion vehicles, but they present a lower centre of gravity location and proportionally lower values of the moments of inertia.

After a severe lane change, a wind gust, or another disturbance, the driver might be unable to recover the intended motion. Even though this fact is known by any driver, the scientific investigation and testing on this phenomenon is just at its very beginning, as a literature review, focusing on SAE Mobilus® database, reveals. We have used different mathematical models of car and driver for the basic description of car motion after a disturbance. Theoretical topics such as nonlinear dynamics, bifurcations, and global stability analysis had to be tackled. Since accurate mathematical models of drivers are still unavailable, a couple of driving simulators have been used to assess human driving action. Classic unstable motions such as Hopf bifurcations were found. Such bifurcations seem almost disregarded by automotive engineers, but they are very well-known by mathematicians. Other classic unstable motions that have been found are “unstable limit cycles.” The driving simulator results have been reproduced by experimental tests on track. We have assessed that the driver’s steering action can make the car motion unstable if a proper disturbance has acted. The delay of the driver’s steering action is the primary cause for the generation of limit cycles. Future automated vehicles should be conceived by focusing on the addressed phenomenon.

The paper deals with traffic simulation within roundabouts when both “connected and automated vehicles” (CAVs) and human-driven cars are present. The aim is to present the past, current and future research on CAVs running into roundabouts within the Cooperative, Connected and Automated Mobility (CCAM) framework. Both microscopic traffic simulations and virtual reality simulations by dynamic driving simulators will be considered. The paper is divided into five parts. At first, the literature is analysed using the Systematic Literature Review (SLR) methodology based on Scopus database. Secondly, the influence of CAVs on roundabout-specific design features and configuration is analysed. Gap-acceptance models used to define the capacity of the roundabout, one of its most important key performance indicators, are also presented. Third, the most common simulation software are described and analysed in terms of traffic demand implementation. Then the communication approaches and path management algorithms are studied. An example is proposed on the integration of microscopic traffic simulations and dynamic driving simulators virtual reality simulations. Finally, car following models suitable for roundabout traffic are discussed. There is still a gap between simulations and actual experience. There are reasonable doubts on how modelling and optimizing CAVs’ behaviour into roundabouts in view of CCAM. It seems that Cooperative, Connected and Automated Vehicles (CCAVs), more than simply Connected and Automated Vehicles (CAVs), could optimise traffic flow, safety and driving comfort within the roundabout. A very promising technology for traffic simulation within the roundabout seems the one based on dynamic driving simulators.

Currently, one of the most important challenges in the field of road vehicles concerns the reduction of road accidents and fatalities. The development of new advanced driver assistance or automated driving technologies may contribute to this goal in the future. This research delves into the analysis of Level 4 (L4) automated vehicles (AVs), specifically focusing on the take-over manoeuvre when the AV exits its Operational Design Domain (ODD). It aims to analyse how the take-over changes, considering factors such as the human driver's state, the machine's operation, and the output devices used to alert the driver. To carry out the preliminary tests, an urban road network, including a mini-roundabout, was replicated in the VI-WorldSim environment, and real human drivers experienced the simulation through a dynamic driving simulator. Drivers were assessed qualitatively, using questionnaires to analyse their perception of L4 AVs, and quantitatively, examining the take-over time needed and their heart rate to investigate the physiological response. Preliminary results show that participants perceived the simulation as realistic and immersive, and they reported an ease of use of AVs. Furthermore, physiological data highlighted an increase in heart rate upon the start of take-over, validating the cognitive load of the individual. The study is part of the HL4IT project aimed at supporting the development of Level 4 AVs in an Italian traffic environment.

The MoLAS is a moving laboratory able to fully characterize the tire behavior in the real working environment. The basic structure of the moving laboratory is represented by a semi-trailer. A rotating frame that supports the measuring system is used to set the camber level by using an electric actuator. An electric steering actuation system guarantees high output torque and high output power. A pneumatic actuator is used to apply the vertical load, allowing to generate a large range of vertical force up to SUVs values. A complex driveline including an internal combustion engine (ICE) coupled with the gearbox and an electromagnetic (EM) retarder is used to apply both driving and braking torques. This aspect constitutes a new feature of the system.

Design of electric motors, especially for automotive applications where early design choices have significant impacts on the final results, in terms of both cost and performances, is a matter of primary importance, with direct consequences on the entire vehicle. Common practice lacks simple, yet reliable, analytical method to evaluate vibration and noise emission of permanent magnet synchronous motors (PMSMs), and this is the gap that the work here proposed aims to fill. In particular, electric vehicles’ noise requirements have added a design opportunity to manufacturers, which, depending on the type of costumers they are selling their products to, need to comply with different preferences. Accurately estimating noise emissions of such complex machines is a difficult matter, which can be fully exploited only at the end of the design process. The article aims to provide a simple, yet accurate enough, tool to estimate the noise emission of electrical motors at the early stage of the design, giving engineers and researchers a tool to drive their choices. An equivalent curved beam model is used for modeling the structural vibration of the stator when subjected to electromagnetic forces. The sound pressure amplitudes are analytically derived based on the acoustic solution for infinitely long cylindrical radiators. Part of the innovation lays on the fact that the contributions of both the radial and tangential forces are taken into account, and a discussion on the effect and influence of the latter on the stator acoustic emission is presented. The sound pressure radiated from the outer surface of the stator is calculated, and a unique indicator of sound emission, named sound pressure level (SPL), is determined. The proposed method is validated against data of two PMSMs from literature, showing good agreement with the experiments, proving the method is a reliable tool for electric motor designers to be used especially during the early stage of design.