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Steer by wire (SbW) system is examined, considering the positive effects of the lack of direct mechanical connection between steering wheel and rack. SbW system's steering wheel has to generate a resistant torque which adds to the friction one. Such torque must be felt as natural by the average driver and carry information about vehicle dynamic condition. System prototype is obtained from a classical steering system. Steering wheel is linked to a brushless 12V DC current electric motor designed to develop resistance torque, after steering column is removed, triple stadium planetary gear is necessary to increase the torque output. A hardware in the loop test bench is realized in order to test feedback torque generation and steering wheel efficiency influence on vehicle behaviour. Steering wheel is fixed to the bench and its rotation acquired by an optic encoder. Steering wheel angle is used as input for a ten degrees of freedom vehicle model through an acquisition data board.

Brake systems represent important components for passenger cars since they are strictly related to vehicle safety: Anti-lock Braking Systems (ABS) and Electronic Stability Control (ESC) are the most well-known examples. The paper is focused on the characterization of the braking hydraulic plant and on the design of a pressure following control strategy. This strategy is aimed at pursuing performances and/or comfort objectives beyond the typical safety task. The low-level logic (focus of the paper) consists of a Feedforward and Proportional Integral controller. A Hardware In the Loop (HIL) braking test bench is adopted for pressure controller validation by providing some realistic reference pressure histories evaluated by a high-level controller. Results prove that innovative control strategies can be applied to conventional braking systems for achieving targets not limited to braking issues, i.e., comfort or NVH tasks.

The superior mobility of a military vehicle provides the combat crew with a tactical advantage through increased cross country speed. The suspension system plays a fundamental role in evaluating a vehicle mobility. A mathematical model that allows realistic simulations of vehicles operating in a wide spectrum of environmental conditions may help to lower costs and time required during their development. The paper concerns with vehicle-terrain interaction modeling, for a military tracked tank, through multi-body and block-oriented approaches. It is focused on the consequences that the suspension system has got on the comfort and on the performance. Thus through a multi-body software a realistic three dimensional model of a tracked fighting vehicle is developed. This virtual model confirms some experimental data available on its longitudinal dynamics. In order to simplify the multi-body simulations, a block-oriented approach is adopted to develop a model of the same vehicle.

Product development in automotive industry is still deeply based on experimentation: test benches and road test facilities are used both for components testing and models validation. Nevertheless a growing role is played by numerical simulation and nowdays by virtual experimentation. The latter is required by the increasing complexity of the systems and cost saving. Moreover new products involve a higher level of integration between mechanics, electronics and computer science, which makes difficult a rapid and low cost prototyping. The design of the vehicle is currently applied to the overall system instead of assembling subsystems separately developed and tested. This approach requires that the same level of integration is achieved on numerical codes and simulators, to be able to operate hardware and software for virtual experimentation in mechatronic systems. This paper briefly describes the experience done since few years, by Fiat Auto and Politecnico di Torino (Dept.

The paper shortly describes an ABS/ESP Hardware-In-the-Loop (HIL) test bench built by the Vehicle Dynamics Team of the Department of Mechanics of Politecnico di Torino. It consists of a whole brake system, integrated through specific interface (e.g. wheel pressures signals) with a vehicle model running in real time on a dSPACE® board. Different commercial ABS strategies are compared, in a large spectrum of manoeuvres: slow brake apply manoeuvres, panic brake manoeuvres, μ-split brake manoeuvres, brake manoeuvres with a sudden variation of the friction coefficient between tyres and ground. The paper deals with the generation of all the signals required for activating a commercial ESP: steering wheel angle, body yaw rate, body lateral acceleration, engine control, etc… Some of them are transmitted by CAN. Typical handling manoeuvres are used to test the ESP: step steer, double step steer, ramp steer, etc… Several brake manoeuvres are simulated while turning.

Firstly, the paper presents Politecnico di Torino Hardware-in-the-Loop (HIL) brake systems test bench. Secondly, it describes in detail all the necessary basic tests to characterize, on the bench, an ESP hydraulic unit: for example, step response of each valve, measurement of pressure limiter valves calibration, step response of motor pump unit. The experimental results are reported. Thirdly, the paper deals with the frequency response of ESP valves, by using Pulse Width Modulation. Pressure gradients and pressure oscillations obtained in the tests are commented in detail. An open loop actuation strategy for ESP is presented, permitting to obtain, in each condition, the desired wheels pressure levels, without having any output pressure sensor in the hydraulic unit. This strategy was conceived by simulation and then successfully tested on the bench. An ESP control strategy, complete of a diagnostic algorithm, was added to the actuation logic described before and tested on the bench.

The paper discusses a gearbox design method based on an optimization algorithm coupled to a fully integrated tool to draw 3D virtual models, in order to verify both functionality and design. The aim of this activity is to explain how the state of the art of the gear design may be implemented through an optimization software for the geometrical parameters selection of helical gears of a manual transmission, starting from torque and speed time histories, the required set of gear ratios and the material properties. This approach can be useful in order to use either the experimental acquisitions or the simulation results to verify or design all of the single gear pairs that compose a gearbox. Genetic algorithm methods are applied to solve the optimization problems of gears design, due to their capabilities of managing objective functions discontinuous, non-differentiable, stochastic, or highly non-linear.

The paper presents a 4-wheel-steering (4WS) control strategy devoted to reduce the turn diameter for small longitudinal speed values and to obtain a yaw rate damping effect in dynamic manoeuvres. Moreover, the 4WS active system conceived produces compensation both for lateral wind and road irregularities. The main results obtained through a functional vehicle model are presented. 4WS was integrated with a Vehicle Dynamics Control (VDC), which was improved for turn while braking manoeuvres. The results due to integration were very good, with a reduction of both systems interventions. Finally, a VDC-4WS-Active Roll Control (ARC) integration was tried, based on only one reference body yaw rate for all the active systems. The main results obtained are presented and discussed.

This paper explores the potentiality of reducing noise and vibration of a vehicle transmission thanks to powertrain control integration with active braking. Due to external disturbances, coming from the driver, e.g. during tip-in / tip-out maneuvers, or from the road, e.g. crossing a speed bump or driving on a rough road, the torsional backlashes between transmission rotating components (gears, synchronizers, splines, CV joints), may lead to NVH issues known as clonk. This study initially focuses on the positive effect on transmission NVH performance of a concurrent application of a braking torque at the driving wheels and of an engine torque increase during these maneuvers; then a powertrain/brake integrated control strategy is proposed. The braking system is activated in advance with respect to the perturbation and it is deactivated immediately after to minimize losses.

To optimize a shift transient during clutch engagement (third phase of a gearshift) it is fundamental to define the engine velocity reference and the more appropriate instant at which to begin the clutch engagement itself. An analytical procedure to calculate the engine velocity reference value during the third phase of a gearshift and the moment when to begin the clutch engagement is presented. Simulation results obtained considering upshift and downshift with engine torque either applied or not are presented. The analytical solution presented permits to tune the third phase of the gearshift in an easier way than previous strategy based on look-up tables.

The first step toward a braking system ‘by wire’ is Electro-Hydraulic Braking System (EHB). The paper describes a method to evaluate through virtual experimentation the actual improvement in vehicle behaviour, from the point of view of both handling and comfort, including also pedal feeling, due to EHB. The first step consisted in modelling the hydraulic unit, comprehensive of sensors. Then it was conceived a control logic devoted to medium-low intensity braking manoeuvres, without ABS intervention, to determine an optimal braking force distribution and pedal feeling depending on the manoeuvre. A failsafe strategy, complete of on board diagnosis, to prevent dangerous system behaviour in the eventuality of a component failure was carried out and tested. Finally, EHB wheel pressure sensors were used to improve both ABS performance, increasing the adherence estimation, and Vehicle Dynamics Control (VDC) performance, through a more precise actuation.

The paper describes the aims, the basic principles and the internal layout of Dual Rate boosters. It presents two models of Dual Rate boosters capable of reproducing their behavior in semi-stationary and dynamic conditions. The models can be adopted to evaluate the effect of the main parameters on the performance of the entire component. A sensitivity analysis is presented. Some comparisons between the performance of Dual Rate and Emergency Valve Assistance (EVA) boosters are dealt with, on the basis of experimental tests.

The paper deals with a method implemented to study braking systems design, modelling components' characteristics through commercial software. It summarizes the potential improvement possible by using modelling techniques in chassis systems design. The first part consisted in producing a passive braking system model. A first validation was carried out on a test bench by using components of different braking systems. Particular attention was devoted to booster modelization both in semi-stationary and dynamic conditions. The second part was callipers, roll-back and thermal phenomena modelization. Finally, it were modelled Anti-lock Braking System (ABS) and Vehicle Dynamics Control (VDC) Hydraulic Units and their integration with control strategies and with vehicle dynamics model.

Vehicles equipped with Automated Manual Transmissions (AMT) for gear shift control show many advantages in terms of reduction of fuel consumption and improvement of driving comfort and shifting quality. In order to increase both performance and efficiency, an important target is focused on the minimization of the typical torque interruption during the gear shift, especially in front of the conventional automatic transmission. Recently, AMT are proposed to be connected with planetary gears and friction brakes, in order to reduce the torque gap during the gear change process. This paper is focused on a block-oriented simulation methodology developed in Matlab/Simulink/Stateflow® environment, able to simulate the performance of a complete FWD powertrain and in particular to predict dynamic performance and overall efficiency of the AMT with innovative Torque Gap Filler devices (TGF).

Chassis Control Systems development methodology is nowadays strongly based on analyzing performance by using PC vehicle dynamics simulation. Generally, the overall design, test bench and road validation process is continuously accompanied by simulation. The Base Model Simulator was developed by the Vehicle Dynamics Group at the Department of Mechanics of Politecnico di Torino both to satisfy this requirement and for educational purposes. It considers a complete vehicle dynamics mathematical model, including driver, powertrain, driveline, vehicle body, suspensions, steering system, brakes, tires. The Base Model Simulator takes in account the suspensions system elastokinematics, including, for example, automatic computation of camber variation during the vehicle roll motions. Tire model considered are either Pacejka's models or experimental data.

This paper presents the methodology adopted by Politecnico di Torino Vehicle Dynamics Research Team to obtain objective indices for the evaluation of the comfort during the gear change process. Some test drivers and different passengers traveled on a test vehicle and assigned marks on the basis of their subjective feeling of comfort during the gearshifts. The comparison between the most significant subjective evaluations and the experimental values obtained by the instruments located on the vehicle is presented. As a consequence, some indices (based on physical parameters) to evaluate the efficiency and the comfort of the gearshift process are obtained. They are in good agreement with the subjective evaluations of the drivers and the passengers. The second part of the paper presents a driveline and vehicle model which was conceived to reproduce the phenomena experimented on the vehicle. The experimental validation of the model is presented.

A four wheel steer control logic is described. A first control logic release, obtained during previous research activity, is based only on feed forward (F.F.) but is here upgraded merging closed loop control (C.L.). Integration between F.F. and C.L. is described. Rear steering electromechanical actuator frequency response is analyzed, in order to consider its not ideal behaviour during control logic design. Several simulation are performed to qualitatively evaluate the error committed considering an ideal actuator during the control logic design. Specific manoeuvres are chosen to investigate about active system influence on vehicle handling; a 14 degrees of freedom vehicle model is validated in order to compare simulation results with experimental data.

Through a single track model, correspondence between typical frequency analysis coefficients and test driver's opinion developed after experimental tests has been stated. Benchmark analysis of several vehicles, considered significant, has been carried out as well as a sensitivity analysis of vehicle behavior depending on passive design parameters, such as vehicle sideslip stiffness and tyre relaxation length. It led to the definition of the different transfer function capable of describing passive vehicle linear behavior; vehicle performance limits, due to unbridgeable physical phenomenon, has been also considered. 4WS vehicle chance to overcome these limits has been investigated, depending on rear steering control logic complexity. Vehicle frequency response has been then analyzed for different longitudinal velocity, introducing thus the concept of “natural vehicle”. The design of a four wheel steer system control logic, based only on feed forward, is described.

The paper deals with the elaboration of an Active Roll Control (ARC) oriented both on comfort and handling improvement. The ARC determines hydraulically the variation of the equivalent stiffness of the anti-roll bars. The control strategies conceived were extensively validated through road tests managed on an Alfa Romeo sedan. The first part of the paper deals with comfort improvement, mainly consisting in an absence of bar effect during straight-ahead travel and in a modification of the roll characteristic of the car. To increase driver's handling feeling, it was necessary to optimise the ratio between front and rear roll stiffness. This purpose can be reached through control strategies based exclusively on lateral acceleration. Some control strategy corrections were necessary to optimise roll damping and front/rear roll stiffness balancing.

A prototype vehicle (PV) is equipped to test powertrain and active chassis systems with innovative control strategies for safety and energy saving. Additional sensors installed on-board allow the measurement and estimation of new information useful to the vehicle dynamic control. The PV was based on a serial production passenger car with Electronic Stability Control (ESC). Testing activities on Controller Area Network (CAN) and ESC Electronic Control Unit (ECU) are carried out to compare the vehicle dynamic performance obtainable using serial production rather than customized control strategies, while maintaining the same hardware. The PV is also utilized to provide reverse engineering analysis about the implemented control strategy for the ESC working in serial production mode.