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Technical Paper

Multi-body Versus Block-Oriented Approach in Suspension Dynamics of a Military Tracked Tank

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.
Technical Paper

Modelling Vehicle Dynamics for Virtual Experimentation, Road Test Supporting and Dynamic Control

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.
Technical Paper

Hardware-In-the-Loop to Evaluate Active Braking Systems Performance

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.
Technical Paper

Four-wheel-steering Control Strategy and its Integration with Vehicle Dynamics Control and Active Roll Control

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.
Technical Paper

Enhanced Tire Brush Model for Vehicle Dynamics Simulation

The aim of this paper is the conception of a tire model which allows a good fit with the physical experimental behavior of the component. In the meanwhile, the model should be simple enough to permit real time vehicle dynamics simulation, in the same way as the diffused Pacejka's model. The paper discusses the influence of the model for the estimation of contact patch properties on the overall tire forces and moments. It demonstrates that unrealistic models of the contact patch can lead to a good fit with the experimental data (in terms of forces and self-aligning moment), even if the real physics of the tire is not reproduced. A realistic model implies a significant reduction of the stiffness of the brushes as a function of the vertical load between the tire and the road surface.
Technical Paper

Electro-Hydraulic Braking System Modelling and Simulation

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.
Technical Paper

Driveline Layout Influence on Four Wheel Drive Dynamics

The paper presents the research activity managed to investigate the dynamics of a 4WD vehicle equipped considering drivelines with different layout. The procedure developed required to conceive an on purpose simulator to compare performance through virtual experimentation. Drivelines mechanical main characteristics and performance increasing due to control strategy were evaluated. Preliminary road test were performed with a single driveline layout, to evaluate simulation reliability and limits. The paper presents the 4WD vehicle simulator, the main equations applied to model open, torque sensing and limited slip differentials, some preliminary road test results showing torque sensing driveline performance.
Technical Paper

Braking System Components Modelling

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.
Technical Paper

Base Model Simulator (BMS) - A Vehicle Dynamics Model to Evaluate Chassis Control Systems Performance

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.
Technical Paper

An Objective Evaluation of the Comfort During the Gear Change Process

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.
Technical Paper

Active Roll Control to Increase Handling and Comfort

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.
Technical Paper

A Methodology to Investigate the Dynamic Characteristics of ESP and EHB Hydraulic Units

The paper deals with the Hardware-In-the-Loop based methodology which was adopted to evaluate the dynamic characteristics of Electronic Stability Program (ESP) and Electro-Hydraulic Brake (EHB) components. Firstly, it permits the identification of the time delays due to the hardware of the actuation system. Secondly, the link between the hardware of the hydraulic unit and a vehicle model running in real time permits the objective evaluation of the performance induced by the single components of different hydraulic units in terms of vehicle dynamics. The paper suggests the main parameters and tests which can help the car manufacturer in evaluating ESP hydraulic units, without expensive road tests.
Technical Paper

A Failsafe Strategy for a Vehicle Dynamics Control (VDC) System

The paper presents a failsafe strategy conceived for a Vehicle Dynamics Control (VDC) system developed by the Vehicle Dynamics Research Team of Politecnico di Torino. The main equations used by the failsafe algorithm are presented, especially those devoted to estimate steering wheel angle, body yaw rate and lateral acceleration, each of them fundamental to correctly actuate the VDC. The estimation is based on redundancy; each formula is considered according to a weight depending on the kind of maneuver. A new recovery algorithm is presented, which does not deactivate VDC after a sensor fault, but substitutes the sensor signal with the virtually estimated value. The results obtained through simulation are satisfactory. First experimental tests carried out on a ABS/VDC test bench of the Vehicle Dynamics Research Team of Politecnico di Torino confirmed the simulation results.