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Journal Article

The Application of Control and Wheel Torque Allocation Techniques to Driving Modes for Fully Electric Vehicles

The combination of continuously-acting high level controllers and control allocation techniques allows various driving modes to be made available to the driver. The driving modes modify the fundamental vehicle performance characteristics including the understeer characteristic and also enable varying emphasis to be placed on aspects such as tire slip and energy efficiency. In this study, control and wheel torque allocation techniques are used to produce three driving modes. Using simulation of an empirically validated model that incorporates the dynamics of the electric powertrains, the vehicle performance, longitudinal slip and power utilization during straight-ahead driving and cornering maneuvers under the different driving modes are compared.
Journal Article

Optimal Wheel Torque Distribution for a Four-Wheel-Drive Fully Electric Vehicle

Vehicle handling in steady-state and transient conditions can be significantly enhanced with the continuous modulation of the driving and braking torques of each wheel via dedicated torque-vectoring controllers. For fully electric vehicles with multiple electric motor drives, the enhancements can be achieved through a control allocation algorithm for the determination of the wheel torque distribution. This article analyzes alternative cost functions developed for the allocation of the wheel torques for a four-wheel-driven fully electric vehicle with individually controlled motors. Results in terms of wheel torque and tire slip distributions among the four wheels, and of input power to the electric drivetrains as functions of lateral acceleration are presented and discussed in detail. The cost functions based on minimizing tire slip allow better control performance than the functions based on energy efficiency for the case-study vehicle.
Journal Article

Drivability Analysis of Heavy Goods Vehicles

The paper presents linear and non-linear driveline models for Heavy Goods Vehicles (HGVs) in order to evaluate the main parameters for optimal tuning, when considering the drivability. The implemented models consider the linear and non-linear driveline dynamics, including the effect of the engine inertia, the clutch damper, the driveshaft, the half-shafts and the tires. Sensitivity analyses are carried out for each driveline component during tip-in maneuvers. The paper also analyses the overall frequency response using Bode diagrams and natural frequencies. It is demonstrated that the most basic model capable of taking into account the first order dynamics of the driveline must consider the moments of inertia of the engine, the transmission and the wheels, the stiffness and the damping properties of the clutch damper, driveshaft and half-shafts, and the tires (which link the wheel to the equivalent inertia of the vehicle).
Technical Paper

Chassis Torsional Stiffness: Analysis of the Influence on Vehicle Dynamics

It is universally recognized that torsional stiffness is one of the most important properties of a vehicle chassis, [ 1 ]. There are several reasons for which high chassis stiffness is preferable. Lack of chassis torsional stiffness affects the lateral load transfer distribution, it allows displacements of the suspension attachment points that modify suspension kinematics and it can trigger unwanted dynamic effects like resonance phenomena or vibrations, [ 2 ]. The present paper introduces two analytical vehicle models that constitute an efficient tool for a correct evaluation of the main effects of chassis torsional stiffness on vehicle dynamics. In the first part an enhanced steady-state vehicle model is derived and employed for the analysis of the vehicle handling. The model takes account of chassis torsional stiffness for the evaluation of the lateral load transfer and, by means of the concept of the axle cornering stiffness, includes the effects of tire non-linear behavior.
Technical Paper

Linear Analysis of the Effect of Tire Dynamics on the Overall Vehicle Performance

The purpose of this paper is to deal with the frequency response of rigid and articulated vehicles subjected to a steering input. In particular, the effect of tire dynamics is considered in detail. Tire delays in lateral force generation can be modeled by adopting first or second order transfer functions. The paper compares the structure of the overall transfer functions simulating the entire vehicle. The results related to three alternative linear vehicle models are presented, in order to draw some objective conclusions about the real effect of relaxation length at low and average velocities.
Journal Article

Vehicle Simulation for the Development of an Active Suspension System for an Agricultural Tractor

The design of suspension systems for heavy-duty vehicles covers a specific field of automotive industry. The proposed work focuses on the design development of a front controllable suspension for an agricultural tractor capable to satisfy the system requirements under different operating conditions. The design of the control algorithms is based on the developed multibody model of the actual tractor, including the pitch motion of the sprung mass, the anti-dive effects during braking and forward-reverse maneuvers and the non-linear dynamics of the actuation system. For an advanced analysis, a novel thermo-hydraulic model of the hydraulic system has been implemented. Several semi-active damping controls are analyzed for the specific case study.
Technical Paper

Racing Simulation of a Formula 1 Vehicle with Kinetic Energy Recovery System

This paper deals with the development of a Lap Time Simulator in order to carry out a first approximate evaluation of the potential benefits related to the adoption of the Kinetic Energy Recovery System (KERS). KERS will be introduced in the 2009 Formula 1 Season. This system will be able to store energy during braking and then use it in order to supply an extra acceleration during traction. Different technologies (e.g. electrical, hydraulic and mechanical) could be applied in order to achieve this target. The lap time simulator developed by the authors permits to investigate the advantages both in terms of fuel consumption reduction and the improvement of the lap time.
Technical Paper

Shock Absorber Thermal Model: Basic Principles and Experimental Validation

The paper deals with the shock absorber model conceived by the author. It is implemented on the basis of an existing shock absorber model already presented by the same author [1]. The enhanced model permits a first approximation estimation of the average temperature of the different components of a monotube or a twin tube shock absorber. The fluid dynamic input data for the model, expressed in terms of pressure drops vs. flow rates, can be parameterized as a function of the estimated temperatures of the fluid through the considered orifice. The process required for the experimental data acquisition for the model is described, as well as the experimental validation of the model.
Technical Paper

Friction inside Wheel Hub Bearings: Evaluation through Analytical Models and Experimental Methodologies

This paper presents an experimental methodology which can be adopted to measure the friction torque of the bearings in the wheel hubs of passenger vehicles. The first section of the paper highlights the reasons why an experimental device is necessary to have an objective evaluation of the performance of the bearing in terms of friction. In particular, the high level of approximation of the current formulas for the estimation of the friction inside a single bearing is discussed and demonstrated. An analytical methodology for the evaluation of the distribution of the axial load between the two bearings of the wheel hub is presented. However, its practical application for the precise calculation of the distribution of the load has to be checked through experimental tests.
Technical Paper

Shock Absorber Modeling and Experimental Testing

Simulation is becoming the fundamental tool to design the main components of a vehicle. The paper describes the shock absorber model which was implemented by the Vehicle Dynamics Research Team of Politecnico di Torino. It is a modular model which can be adopted both for mono-tube and twin-tube shock absorbers. It can be used at different levels of approximation, as a function of the kind of user and his/her targets. The main data which have to be inserted in the model are fluid properties, the basic dimensions of the component and the characteristics of the orifices of the shock absorber. An experimental test bench was conceived to obtain the diagrams plotting flow rate through an orifice of a shock absorber versus the pressure drop between input and output ports. The test rig and the procedure to perform the experimental tests and insert the results in the shock absorber model are described in detail.
Technical Paper

Electro-Mechanical Active Roll Control: A New Solution for Active Suspensions

The paper presents the approach followed by Politecnico di Torino Vehicle Dynamics Research team to design an electro-mechanical Active Roll Control (ARC) system. The first part of the paper describes the targets of the system, which has to improve both comfort and handling. Different solutions for the implementation of the electro-mechanical actuation were evaluated. A prototype of the electro-mechanical Active Roll Control was built and experimentally tested in the Vehicle Dynamics Laboratory of the Department of Mechanics of Politecnico di Torino, by adopting a Hardware-In-the-Loop (HIL) test bench. The experimental results show the benefits of the system, both in a stand alone configuration and integrated with an Electronic Stability Control (ESC) system.
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

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

Hardware-In-the-Loop (HIL) Testing of ESP (Electronic Stability Program) Commercial Hydraulic Units and Implementation of New Control Strategies

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.
Technical Paper

Hardware in the Loop for Braking Systems with Anti-lock Braking System and Electronic Stability Program

The paper describes Politecnico di Torino braking systems test bench, based on hardware in the loop (HIL). The test bench, consisting of the whole braking system hardware, can be used for: Analysis of passive braking systems, to determine the main characteristics both in semi-stationary and dynamic conditions; Analysis of passive braking systems, to investigate the influence of eventual asymmetries on vehicle behaviour, since a vehicle model runs in real time and receives wheels pressure values by the sensors on the physical device; Analysis of Commercial Anti-lock Braking/Electronic Stability Program (ESP) Systems, both from the point of view of control strategies and hydraulic units performance; Definition of new ABS/ESP control strategies, e.g. considering wheels caliper pressure signals as inputs, using pre-existing commercial hydraulic units.
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

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

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.